Yeah I know it can be a bit daunting if you don't have things backed up and prepared beforehand.
I have it backed up but my prep is usually missing something, like I'll have it all on my NAS, but then I'll forget I need to install network drivers or something so it can't see my NAS.
But there's:
Windows install and configure all the setting (temp directories, swap files, location of Documents, Downloads, Videos, Start Menu, Desktop, etc.)
Drivers and associated utilities, which might also need some configuration
Fan control software, temp monitor software, overclocking software (which might be the same thing) and configuring them.
Anti-Virus and setting exceptions
Firewall and setting up rules
Handbrake, configuring and importing profiles
OBS, config and importing scenes
IDEs and such
Web browser, config and importing favourites, open tabs and installing and configuring plugins
E-mail client install and config
Copying over documents, downloads and save games (which vary in location based on the game)
Then you have to install your launchers (Steam, EPIC, Battle.net, EA, Ubisoft, GOG, Battlestate, etc.), configure them
Then re-install all the games (even if they're installed you need to get the launchers to realise they're there) and configure them, install mods, etc.
VoIP apps and such (install + config)
VR and VR games (install and setup)
And even them I'm sure I'm forgetting stuff.