I haven't been on a train but I live 5 minutes from a busy station in Fife, heavily used by commuters to Edinburgh. I pass it fairly regularly at times when it was heaving pre lockdown. It seems to me that it's still very quiet.
Only occasionally and only the Glesga commuter lines, so probably not much use to you, but they've been deserted at times pre covid they'd be rammed in a London Underground-esque fashion
Trains are mostly still fairly quiet, usually able to get a few Windows open depending on age of train, and get a section of the carriage to yourself, 'rush hour' can still be busy but depends on the route.