Questions regarding a "private use only" App/Service

After checking your guidelines for applications, I am quite unsure if these are also applicable for any service or app that you write just for your own usage?
Especially all rules pertaining to (a) registering an App and (b) saving personal data etc. Do I have to follow these as well, when I am only writing a script to download my station's data to a home server within my network at home?
And is there a way to authenticate against the API with my own account without using the 4 Step "Authorization Code Grant" Procedure? This procedure won't work from a Server within a private network at home, as the is no publicly available return URI - and fpr home security reasons there never will be any - and the second authentication method ("Client Credentials Grant) is said to be deprecated since Octor 2022.
Or does the notice that speaks of "data from another user's account" mean that I can still use this when I only connect to my own personal account and weather station? If this is so, do I still have to register a service running in my home for my own station as an app to receive the necessary client_id?