No GUI for grub and no plymouth splash screen

I have just upgraded from Leap 42.3 to 15.0. I had a problem because the installer rightly guessed my machine has UEFI but didn’t notice that I had set the machine up non-UEFI when I first set it up as a Linux workstation in 2016 (I won’t bore you with why). I rescued that but now when I boot grub’s menu is presented on a console screen (retro maybe but not what I want) and plymouth doesn’t work instead I get three little squares, arranged horizontally, that alternate in brightness. I have spent the past hour searching for a way to fix these without luck.
The machine has an Nvidia graphics card, with the proprietary drivers installed. Once the boot process gets to the login screen everything is as it should be (well, apart from Plasma’s inadequacies of course).
Advice on how to regain the graphics for grub and plymouth would be much appreciated.

You can try a forced reinstall (or unconditional update in Yast) of “grub2-branding-openSUSE”.

And maybe also open Yast bootloader. Click on the “Kernel Parameters” tab and make sure that the box “Use graphical console” is checked.

I’m not sure about the plymouth problem. I think some other users of Nvidia graphics are having that problem. You could try a forced reinstall of plymouth, but it might not help.

ISTR mailing list mention that proprietary NVidia drivers became incompatible with Plymouth.

Yes, that was selected already.

This did indeed give me back the graphical menu, but it seems to draw more slowly than it used to (Leap 42.3). I can live with that.

I did that too but without any effect.

I guess that’s it. I wasn’t sure if the drivers had even been installed at the time plymouth started but perhaps they are and plymouth can’t use them. I’ll have to live with that.

Thanks. nrickert’s response says that too so I guess it must be the general view (unless someone else responds to my original post with a workaround).