I have checked two Tumbleweed installations with Intel graphics, and Plymouth is now working fine on those. I also have Tumbleweed installed with QEMU/KVM (as a virtual machine). Plymouth is broken there. I set the VM up to use an encrypted LVM. The plymouth screen prompts for the encryption key. But what I type at the keyboard is ignored. I have to boot without "splash=silent" on the kernel line, to get a text virtual console where I am able to provide the encryption key. So maybe plymouth has trouble talking to the "spice" graphics.