Obligatory Worse Is Better by Richard P. Gabriel reference
TL;DR for those unfamiliar: the guy (an important figure in programming/Lisp history) argues with himself for a few decades over what’s the better of two different approaches to software development: good-enough but hacky/limited/worse software tends to outcompete more complete/elegant/correct software because it gets to market quicker and makes iterative growth from there. Essential reading for anyone interested in programming history, or just software in general.
Kinda depends on exactly how much you want it to sync, e.g. should it truly sync all files from the synced volume to all clients, or do you want the files to only sync/download to clients when requested, keeping a “master copy” on a server?
For me, I use Syncthing for a simple setup where I want multiple machines to have a few different shared folders that sync with each other, all files updated on-disk when connected to a network.
For a more Google Drive-style approach with only fetching/syncing files onto client disk when explicitly chosen, I believe Nextcloud has what you need, but I’ve not used it on any of my own machines. It can be self-hosted or paid for, depending on what you prefer.