Finally after 4 months I managed to get Rockstar to sort my account issues and I'm able to play The game now.
Anyone running any of the graphical and RTX mods? Whats best and easy to install?
I've recently started playing through single player again and using Natural Vision Remastered.
There is also Natural Vision Evolved, which I believe is newer and slightly better looking, both are available here:
https://www.razedmods.com/gta-v
I know you only mentioned single player, but please be aware that with any mods installed you cannot play GTA:Online as it'll probably get you banned.
The reason that I went with Remastered was that Evolved is currently single player only, with other features behind a patreon paywall and I may decide to play unofficial multiplayer (using the FiveM client) again in the future - NMR includes the config/plugin for this.
Installation wasn't all that difficult, just follow the instructions in the included HTML file. You'll also need to install some pre-requisites including OpenIV.
Once you have it installed there are customisations you can make to tweak it to your liking, but I so far haven't bothered with that and it looks great. It mainly improves things like reflections and the lighting/weather effects, although there is a slight bug in that it makes some characters in mission cutscenes too bright which looks a bit odd!