Not the OP but I run a personal server for mail etc., and I do remember one LTS → LTS upgrade of Ubuntu that removed the DKIM milter that my postfix config depended on.
So it happens.
> You might want to look into "DevOps". The idea is that you script your deployments together with automated tests for them
For a personal server the things that in my experience break are related to configuration files.
This can be subtle things, like some new option enabled by default that conflicts in some edge case, it can be upgrade scripts that butcher existing customized configuration files, or it can be a total restructure of how a package has structured its config.
All of this has happened to me, and I don’t think having scripts able to redeploy my server would have been of any help resolving these issues.