I've read here that silencers are not compatible with revolvers.
The question of why that might be so has bugged me since I read it.
Why is that so? Does it have something to do with clearance between
cylinder (chamber) and barrel?

How about rifles that are not gas-actuated semiautos, i.e. bolt,
lever or pump actions? Perhaps it's not feasible to effectively
suppress the report of a rifle with supersonic muzzle velocity, which
(I think) includes most modern centerfire rifles.

I certainly have no need or desire for a silencer, but I'm curious.