Screen Saver bugs were not fixed in Big Sur 11.2.2 (e.g. arrow keys do not work like they did before, etc.)

If you want to display your images full screen and maintain forward/back/pause/start control over then the create an slide show in Photos and run it full screen. You can set the on screen time to whatever you want and use the arrow keys to go forward or back and the space bar to stop and go.

Log your feedback where the folks at Apple might see it: Product Feedback - Apple

If alternative screensaver apps are an option, JWZ maintains the classic and canonical X screensaver collection, and has a macOS port available:

https://www.jwz.org/xscreensaver/

I would not call it a bug - it is probably the expected behaviour, after removing previously supported features.

I find it even worse, that we no longer can display the filenames or titles with our photos in the screensaver, like we could many system versions before.

I have switched to "ArtSaver" as my screensaver. I am not sure, if there is already a Big Sur version of this useful screensaver. I have only used it on Mojave and Catalina.

See: http://www.cs.uni-bremen.de/~zach/software/ArtSaver/index.html

Thank you for the link - it has been a while that I used macOS ports. Is there a slideshow screensaver included? I am seeing all the great X screensavers in the preview screenshot, but have not seen a screensaver, that will present a folder of images as a slideshow.

GL Slideshow. There are others that show piles or manipulate or transform images. Photopile, Ripples, Flip Screen, etc.

Donno about the available controls with the photo screen savers, as it’s been a decade or two since I was last routinely rummaging the X screensavers, and that was for a copy of Xroach for a prank, and which probably isn’t a screensaver that’ll work with macOS as it needs full control of the display.