Under “Theming”, i could upload my own images. Which Pixel dimensions are the the correct values for Logo and Background Image?
I’m not sure if there are restrictions. Normally there is an automatic rescaling, but in the rescaling procedure, there is a php bug (https://github.com/nextcloud/server/issues/2208), but we have a workaround in the code. Either wait for the next release 10.0.2 or apply this patch manually: