How to make a flushometer toilet look nicer?
Clean and tidy is fine.

Many find the « classic » look engaging, whimsical, different so if they are working leave well alone.

Seriously though, if the toilet is dirty they will complain but I doubt they will complain « nice clean toilet, but I don’t like the flush mechanism »...

So, clean, tidy with good paper and see if you get comments down the line.