I’m in the 4th box where there’s nothing to do so you try something new and botch up systemd or netplan or something enough to warrant a fresh install and start again
Dude it sounds you're over skilled for the job. You just need to read some guides and you probably know already how networking works, very basic linux commands, linux folder structures, and then the concept of docker - primarily how it maps networking & folders from your "host machine" to the "docker container", and how it loads services using a docker compose file. Especially for nextcloud, domain dns management and dynamic dns etc would be very helpful knowledge.
Also, just a suggestion, chatgpt etc are super useful. You tell them what you want and it spits out custom instructions for your setup, and you're able to counter question at any point. If it does make mistakes, which it will, it's a learning opportunity for you to troubleshoot and figure out how everything works. All the best and if you have a question feel free to message me.
Tiktok got banned in India some years ago and it doesn't work if you sideload, or even VPN somehow. But pretty much the next day instagram launched their reels things and people jumped ship without talking about tiktok anymore...
Tinkering is honestly the best part about 3d printing!