I tend to use cards, but I don't always use end screens because I know that they don't show up on the devices. However if it won't cover up some important information for your audience on that last 5 seconds of the short (minimum that the end screen can be) - then go ahead and add it. Keep in mind that your short must be at least 25 seconds or longer in order to have an end card added. People that are looking at shorts are generally swiping to move to the next video quickly even before the end card shows up honestly.
Honestly I have never seen end screen or cards on shorts video. There are few of my favorite creators I usually watch until the end but I was not aware we can use end screen on shorts video? I though end screen can be shown minimum of 30 seconds before the video ends so does that really add any value if used in shorts?
The way I see it, if YT gives you the option to add those, you must try to add them. If for whatever reason they didn't want to have them there, they would have taken them out. Who knows what they have in mind next...?
Thank you for your inquiry related to our bulk-editing features. Unfortunately, there have been some changes to our system (and some industry changes in general) that are going to prevent us from continuing to providing these card and end-screen related features. We are doing everything possible to give our users the best available services and exciting, new tools are continuously being developed and we promise to remain on the cutting edge of what is available to be provided in order to ensure that we remain at the forefront of what can be done to help you succeed and thrive on your YouTube journey.
But there is a silver lining; card/endscreen templates make the upload and best-Practices process easier and more streamlined but they do not promote the sort of engagement that you are looking to achieve with these features. Rather than simply checking-off the Best Practices and moving on we are going to actively encourage users to utilize these elements for more natural, intentional purposes. They will need to be set manually in your content but a card that pops up at a specific point in a video where the creator is providing a Call-To-Action (CTA) for the viewer to engage with a link or a different video/playlist are far more effective than a card that simply pops up on screen. The same holds true for end screens.
It is unfortunate that this tool is no longer available... but in all honesty this should very easily be a net-gain for any creator who is now going to take the time to put more emphasis on the value a planned and placed card or end screen can provide.