I’m gonna start using NixOS as my daily driver in a short time, may I ask whether you can pinpoint me to that part which needs to click? Is it learning Nix/being able to write derivations? (also learning resources etc.)
Nix is basically the future of operating systems. The one problem that still needs solving, which is blocking wider adoption, is ease of use. People are working on making the command line tools easier, but what will really do it is something that abstracts away config generation with a UI installer and tools, but opens up the config if you go into "advanced mode" or something like that.
1. Use flakes to set up your system and do work with. It sometimes feels underdocumented, but it's worth some headscratching imo.
2. Don't worry about putting everything in the base system. Stick to services (Tailscale, Syncthing, etc) and system/base desktop software. It's easy enough to use nix run, or Podman, or flatpak, or even AppImage to a degree.
3. Want to configure something declaratively? Before pulling out HomeManager or another user tool, consider configuring software at the system level. I do this for Zsh, SwayWM, etc. As a bonus, you can easily block off shell startup files and chown them to root so that malware can't trivially insert themselves there. (It's a weak protection, but definitely doesn't hurt in addition to other approaches.)
There's more (I recommend using Nix-ld to support AppImage and raw binaries better) but these things go a long way.
Helps to get some intuition on what fits where.