Hi, Let's see if I can ease your pain. Unfortunately not all apps are working well with Android 11 because some developers are particularly slow to update. This applies mainly to social media apps (or at least they are the most mentioned!) There's not a lot Samsung can do about these as it is not their intellectual property.
There are certain things Samsung could have dealt with better. Firstly, you are right about Gallery, very little functionality but the aim of gallery was merely to display all photos and videos on a device which they seem to have reverted back to. Now, as you say you have to open the file in video player for the drag bar. In Videoplayer the image capture button is now on the top left of the video. When you press this you will get a small picture on the video, showing what you have captured. While I think if it, the odd thing is in the photos app the drag bar is there but no image capture button!
Yes, they have messed up the calendar app by removing the custom setting. As a way around this, use the reminder app. Just ask it to create a reminder for every three weeks from xxx date.
I hope this helps a little.