I've done the same for a long time. I've tried so many purpose-built alternatives, and always come back to my solution. (Funny enough, Microsoft Money from 20+ years ago is closer to what I'd like than anything available today)
Not to say there aren't features I wish I could easily have. I could of course build it, and I've "started" so many times, but after a few hours of the typical boilerplate code you have to deal with, I'd always give up and go back to my surefire solution.
(This was before vibe coding, so I may take a stab at that)
I have an Expense Tracker UI within Google Sheets that allows me to submit expenses to the main sheet (currently just over 5000 rows of expenses over the last few years)
I only just recently vibe coded a web UI tool that uses a Google Service Account to add expenses to this Google Sheet for me, and then created a Progressive Web App from that so I could do everything on my phone.
In summary, Google Sheets is sometimes all you need instead of a database for very simple applications (and built for an audience of one)