While booting, hit ‘e’ at the grub prompt. That should get you into an edit screen. Scroll down until you reach a line that begins with “linux” (or maybe “linuxefi”). Scroll right. Delete the text “splash=silent”. Now continue booting (usually CTRL-X or I think F10, but there will be a note on the screen.
Do you now get a prompt for the encryption password? (It will be a text prompt rather than a graphic prompt).
An alternative: Same steps, except replace “splash=silent” with “plymouth.enable=0”. Do you now get a prompt?
By the way, you can make these changes permanent with Yast bootloader (use the kernel parameters tab). But at this stage we are really debugging. Is this a plymouth problem or some other problem.
I’m not using plymouth with Tumbleweed, but I will give it a try in a while to see if I run into that issue.
Maybe I wasn’t clear enough,
I do get a one line shell promt to enter de password for de-crypting the /home partition. But that is a shell promt and not the nice graphic background with text entry field for the password.
Also de-crypting isn’t the problem.
What this implies, is that the plymouth graphics splash screen is not showing. There is, perhaps, a text based plymouth screen as a fallback. Is I recall, that shows 3 green dots, except that the dots might be squares or question marks or some other character.
It’s some kind of graphics driver issue. Maybe you should mention your graphics card, so others with the same card can comment. I have only Intel graphics, and that seems to be working properly at present. Personally, I prefer the text screen with all of those boot messages.