Plymouth animation does not properly load during startup in Ubuntu Unity 22.10

Question

I am using Ubuntu Unity 22.10 in an iMac (late 2011 model). The Plymouth animation does not load during startup, but it does load during shutdown.

How to fix this?

Here is the startup Plymouth screen, which just says "Ubuntu 22.10" on a purple screen.

Here is shutdown screen with a nice logo of Ubuntu Unity.