You are on the wrong website for RMC support.
Jaksta however can capture Youtube shorts. If using auto mode you may need to adjust the min download size in the settings > internet downloads > advanced > https depending on what your browser is streaming as the 3gp is < than the default 200kb size.
I had use Applian's Replay Media Capture (RMC) for years. First they had their own product, then scrapped it to add their frontend to Jaksta, and then dumped everything theirs and went with just reselling Jaksta. I tend to call Jaksta Media Recorder as RMC. Sorry. When Applian went to reselling Jaksta as-is (not their product, no frontend or GUI change, just resell Jaksta straight), the 2 products were identical. I gave up on Applian's resell of Jaksta. Everytime I reported a technical defect, Applian didn't do anything themself, redirected the support request to Jaksta, and I'd have to wait until Jaksta fixed the problem to then have Applian report back to me. I decided to go direct to Jaksta.
I don't see the prompt you show listing multiple formats and quality. Perhaps that's a dialog that gets presented when multiple streams are detected for different formats or qualities in recording. In Jaksta Media Recorder's settings, under Internet Downloads, minimum duration is -1 which presumably means that function or threshold is disabled. Rather than get nuisanced with a list of available formats/quality for multiple streams for the same video, I configured for preferred download quality = highest, and preferred download format = MP4 (and why there is sometimes a "Muxing" state after "Downloading" to convert to MP4 format. Perhaps if preferred download quality = prompt then I'd see the dialog you present. I don't want to get prompted. I want Jaksta to pick whichever stream has the best/highest quality. Since I also selected MP4 for the preferred download format, Jaksta should select amongst those stream in MP4 format, if any (if not any then it should pick highest quality, and follow with the conversion to MP4).
I also went under Settings -> Internet Downloads -> Advanced -> HTTPS. Nothing listed there. No exclusions are listed. I've only gone there to use the Reinstall button to get Jaksta's certificate installed into Firefox's private certificate store (Firefox uses its own cert store instead of the global one you see when using certmgr.msc in Windows). Since I have no entries under HTTPS, I don't know what you expect me to see there. It looks like an exclusion list per the description "Do not pass the following urls through the HTTPS/SSL monitor".
Have you actually visited the URL at Youtube that I gave showing some "shorts"? The web page has several short videos. This is one of those web pages using script to keep enlarging the content. As you scroll to the end or get near the end of the web document, a script loads more contents. Maybe mobile users like ever-scrolling content of infinite length, but it sucks on the desktop rather than using paging or an element to add more content. Maybe Jaksta Media Recorder figures it cannot determine which stream to capture since there are multiple streams due to multiple videos per page, and the video content keeps enlarging when scrolling the web doc. I changed the setting preferred download quality to Prompt, but the screen you showed did not appear listing the available multiple streams for formats and quality.
While Jaksta Media Recorder could prompt for multiple streams on one video, what will it do with an unlimited number of videos per web page?
I did not find an obvious means (provided you Youtube) of displaying a lone video short on its own web page, so JMR would know that's the only video to capture its stream(s). A workaround I found is to right-click on a particular video short (in the web page that lists an unlimited number of them), select "copy video URL" from Youtube's menu, open a new tab in the web browser, and paste the URL into the new tab. That opens the video short in its own web page, and JMR will capture that.
My screenshot shows the detection of a "short". The url you provided.
Prompt shown is only displayed when Settings > Internet downloads > Preferred Download Quality or Format are sent to prompt.
Here is is with highest/mp4 selected, which just downloads.
If you could keep things concise, and provide debug logs that will speed things up.
I've attached the log file. Debug mode was enabled before I visited the multi-video "short" page at Youtube (https://www.youtube.com/shorts/mDnJRdS9Oro).
In the jmrp.exe.log file, I found:
2022-04-02 00:33:21,070  INFO dm [(null)] - HttpsProxyManager: aa744bd1-8664-4c98-863d-f5e65134f215: Request sent: https://www.youtube.com/shorts/mDnJRdS9Oro 2022-04-02 00:33:21,283  INFO dm [(null)] - HttpsProxyManager: aa744bd1-8664-4c98-863d-f5e65134f215: Response: https://www.youtube.com/shorts/mDnJRdS9Oro: HTTP/1.1 200 OK 2022-04-02 00:33:21,283  INFO dm [(null)] - ExtractionEngineDownloader: Checking if supported url: www.youtube.com/shorts/mDnJRdS9Oro 2022-04-02 00:33:21,283  INFO dm [(null)] - ExtractionEngineDownloader: Not supported: www.youtube.com/shorts/mDnJRdS9Oro 2022-04-02 00:33:21,283  INFO dm [(null)] - ExtractionEngineDownloader: Checking if ignored request: www.youtube.com/shorts/mDnJRdS9Oro 2022-04-02 00:33:21,284  INFO dm [(null)] - ExtractionEngineDownloader: Not ignored: www.youtube.com/shorts/mDnJRdS9Oro
In that part of the logfile, I noticed:
Checking if supported url: www.youtube.com/shorts/mDnJRdS9Oro
ExtractionEngineDownloader: Not supported: www.youtube.com/shorts/mDnJRdS9Oro
I don't know the product well enough to know if subsequent lines indicate if JMR attempted other modes to capture, got confused, or gave up.
Add youtube.com/shorts to
Settings > Internet Downloads > Advanced > Extractor > the following urls will be passed to the Extraction Engine if you want to detect them in AUTO mode. Otherwise just enter the url directly.
Log files will only make sense to me.
Sorry, but I'm not sure what, if anything, I'm supposed to do to the Extractor settings. For the https://www.youtube.com/shorts/mDnJRdS9Oro example, am I supposed to add youtube.com/shorts to the "Supported Url" list?
By the way, I wanted to see if there was more info on the Extractor settings, and went to:
Under the "Advanced Internet Downloading Settings" section, that mentions the Page category has this inclusion list. Not shown there are the extractor setting categories. The advanced settings have changed a lot, so this help page needs updating.
Argh, I missed the first line which said "Add youtube.com/shorts to ...". I added that to the inclusion list for supported Urls in the Extractor settings, and it worked. Thanks.
I open the Youtube web page for a video (https://www.youtube.com/shorts/mDnJRdS9Oro), but RMC won't automatically start recording the video (RMC is configured to load with Auto record enabled). Why? Even if I click on the Play button (rightward red triangle icon atop video), RMC still won't record the video.
I did not see an option in the Support button inside of RMC that lets users submit reports of sites by URLs to videos that RMC will not capture either using Auto capture mode, or even when the video is manually started. In the left pane, "Get Support" doesn't offer submissions for URLs where RMC doesn't work. The life preserver icon for "Support" just takes me to a web site where I found no submission report form.
Get started with YouTube Shorts
Introducing the shorter side of YouTube
I've never seen Youtube Shorts videos before, but they can be listed in a search at Youtube.