What are opinions on 2021 upgrade to 2023 vs new full install 2023 and migrate settings and apps on new server. Has anyone done a simple upgrade easily?

For my own sanity I have always, ALWAYS done a fresh install, then set things up, tested thoroughly and then migrated DNS and the like. Backing out of an update is not really easy. Please keep in mind that while there don't seem to be a lot of huge changes visibly, we had to do a ton to integrate Java17, so I highly recommend a full test cycle to make sure nothing is amiss with your appliction.

Agreed, a fresh install is always nice. And if you're using a tool like CommandBox with CFConfig, then it's no big deal. I have dozens of servers on my local machine and I can go right now to any of them and run

server forget --force
server start

and restart a fresh new server and it will all come back exactly as before with all the same settings. When you get to that point of automatability, you stop worrying about ever upgrading a server in place 🙂

I always prefer a fresh install / OS whenever possible