I'm sorry to say it was a bit of a pointless exercise. I uninstalled and reinstalled everything. The update failed again with the Missing files error on both the Planet Coaster 2 and Steam updates. And noticed during this time now that when using Steam to uninstall in the recommended way, the Desktop icon for the game is still there and still tries to load the game and Steam. So I've used Add/Remove programs to get rid of them both again and after yet another attempt at 7.1gb to get the game back, I am back in the position I was at lunch time where neither Steam nor the game will load at all.
I'm never going to believe my PC is at fault whilst only one program is affected, especially given a refresh and restore.
I think I've persisted for long enough but I am struggling with the idea that this might be the end of my 30 year RCT playing. I'd try again maybe at a later date but right now just feeling very burned and let down. 19 hours ago I put my first ever videos on Youtube and now just feel like an idiot. Probs fair to say I've had enough.
Uhm....corrupt files are mostly an indicator of a degrading disk or indication of malware/virus. Especially if you downloaded them serveral times, so a simple transmission error/download couldn't be a thing. I don't want to scare you, but steam not working properly is mostly not a good thing but really messed up. Everyone can hate on steam as much as they want, but their stability is one of the strong suits, if your machine can't handle steam anymore, there might be something wrong in the background.
Also you need to keep in mind, that memory (ram or hard disk) most of the time get faulty over time, it is not one big poof and your pc stopps working, but a slow and degrading process, where more and more issues present them over time.
