Git version control.

Codeberg is another good service I have not seen mentioned yet.

Edit: typo

Yes, using a remote code repository (i.e. git) - plenty of options aside from github.

Merely git pull the repository to whatever machine you want to work on and commit the changes back (rinse, repeat)

Git is the way. I run a Gitea instance so all my code lives on my home server but have used Github in the past.

code goes in git which you can push to other devices and pull from other devices. but if you're not used to it and you turn off a machine and forget to push... you're stuck.

for syncing files in general, I use syncthing. open source, e2e encrypted.

Just use git and a remote repo. Don't need GitHub or anything of that sort.

Git. Git git git.
If it is text and can be modified from multiple places, should have a single "main" branch and feature work done independently on separate "branches". Or even just a "back this up".
Git.

Git is text based version control (tho it will do binary file, just not elegantly).

So yeh, git.
GitHub is easy to host on, but owned by Microsoft and is somewhat proprietary (by the time issues and other enhancements GitHub provides), but at the end of the day it is git with authentication and is on the ol "cloud".
Plenty of ways to replicate this if it's just for you

yes, it is something people generally manage through git. github or gitlab (if you want to avoid microsoft)

Even though there are other ways to solve it, git is the right learning path.

One more thing regarding Git:

You'll likely want to keep your main branch functional at all times, so you would normally wait with your commit and push until a feature is ready. This wouldn't mix well with switching machines at random times.

That's where branches come in handy: create a feature branch, commit and push as often as you want. If the feature doesn't happen to work out, just delete the branch. When the feature is ready, merge the branch into the main branch. There even is an option to squash commits into a single one when merging, so you don't have to keep the whole commit history you created in the feature branch.

I don't think this has been mentioned, but it kind of depends on where your multiple laptops / desktops are. Is this always on your own home network? Because in that case you don't even need a remote service like Github

If so, you can create a network drive on any of the devices - mount the network device on your other devices, and then create a local git repo there. Just remember that using an external git service is also a backup. So if you do everything locally, make sure to have your own backups in place

A much, much worse but also possible solution is to just put your projects into onedrive/dropbox/gdrive and sync it everywhere. It works for syncing, since you're saying that's the main objective - but you lose out on version control

I'll add one more perspective: git is the "right" way to do it, but I'm a lazy forgetful person who wants to work on the laptop but the changes on the desktop aren't committed or pushed remote. What I often do is to use VScode's remote development tools to open a remote connection the last computer with uncommitted changes, and work like that. If I'm headed out, I'll use the remote connection to commit the code so I can access it off my home network via codeberg.org.

Occasionally if I'm already out, I've even used "raspberry pi connect" to remote onto my network, then ssh over to my desktop, then commit and push. Don't do that though. That'd be irresponsible.

I use Mega(sync) to keep my various PCs in sync. Before that I used SpiderOak for a number of years, but the service started degrading at some point, which forced me to switch.

While committing to a git host is not a bad idea, it doesn’t cover all the stuff you might want to sync in my experience

I used to use Dropbox for this, and it works, it's automatic, so you'll have the latest copy without manually pulling changes.

However, for any non-throwaway code i use git now. It gives me granular edit history via commits, branches for experimental changes, and i can push it to github where i can run tests and deployments for free. However if you're using git, you still need to run commit, push, pull commands but if you use an IDE or even a modern editor, it'll have hot keys for it already.

Also there are files you're not supposed to commit, like binaries and 3rd party dependencies so you may need to setup a virtualenv and run pip install on each machine independently.