What's the difference between what you're suggesting here and a password manager? Enxrypted local file, with an optional sync service. I know that if I was setting up my own password manager for security reasons, the sync part is likely the most vulnerable, hence why I would like to offload that to a third party that I trust.
[0] https://bitwarden.com/help/article/what-encryption-is-used/
The ability to port to any alternative tools that provide superior capabilities, should the need arise.
Utilising the file using standard shell tools (gpg piped to grep, sed, awk, etc.).
I've been around long enough to see multiple tools come and go. Even PGP itself dates from after the beginning of my professional career with computers (though near the beginning). There are multiple applications, operating systems, and architectures I've used which have been relegated to the dustbin of history. I'm quite leery of becoming dependent on any one specific application or tool, most especially one that that's not been proven across multiple decades and widely adopted.
PGP, GPG, vi/vim, or emacs would all pass my tests. They're available on any system I could conceivably use. Even iOS, though with some difficulty.
Encrypting and syncing a file is simple.
Managing syncs from multiple locations of an encrypted file is ... a bit more complicated. Git might be able to manage that with some hooks.
I'm a fan of Zettlekasten for notetaking and knowledge management.
Filing passwords on index cards or business cards (3.5x2 in, ~9x5cm), with a sensible indexing system, scales up reasonably well. There's certainly extant physical infrastructure.
The typical person has on the order of about 100 online accounts. Managing even 1,000 accounts in an index card file is at least within reason.
Another alternative is a GPG-encrypted file, though keeping that synchronised between multiple locations might prove a challenge.