What is the best database to use for a self-hosted GIS application?

As I am transitioning out of my father’s appraisal practice and starting my own, I am keen to modernize some of the workflow and build a second-brain to augment my own practice.

Part of this is taking work that we’ve done on spreadsheets and making it so I can have a mapped time series view of changes in the markets I serve (which help me fill out parts of the forms, and have a more informed view of how prices in different areas fluctuate over time/historically/etc). I have a bit of an SQL background, but that was more data wrangling than actual production work, so I fully understand I might not be informed on the best db for my use case.

Having it be self-hosted is my only caveat, as I would need access even if the internet is down, and I don’t trust cloud providers to do a better job than I can (used to work at one, so I am biased in that respect). Would most likely be hosting on a NAS/Synology Box connected to my Desktop.

This would be nothing customer facing and is purely for my office to use as a competitive advantage over the majority of my older peers; Many of which while technically adept to an extent, but whose processes are still tied to “the way it’s always been done”.

If there are any things I can clarify or any additional questions you might have, I’ll be keeping an eye on the thread as I’m researching the houses we’ll be appraising later this week.

Thanks for any input!