You mention exporting files to Nextcloud; Nextcloud also has a Contacts app. I don't save contacts locally anymore. I use Davx for contacts and calendar.

For 2FA, Aegis is great, but I also use self-hosted Vaultwarden for that.

When you mention separate profiles for invasive stuff, Shelter or Insular are good for that.

For the keep it boring part: Null Black Wallpaper in Fdroid. It saves battery life and it doesn't create an emotional connection to your phone.

These are great articles. I already do pretty much everything you post, but I never sat to write the steps down. You're doing a great job!