G'day Les. If you are going to try something with Syncthing (which I have not used) that might jeopardise one or both of your Manjaro and Mint, I woud be inclined to take a full snapshot of each with Timeshift first.
Timeshift is already installed on your Mint, and can easily be installed on Manjaro as well. See my Thread at
https://www.linux.org/threads/timeshift-similar-solutions-safeguard-recover-your-linux.15241/
and ask any questions there.
My 2 cents on cloud - you might read up on Mega
https://mega.nz
They are New Zealand-based and before I get flamed, I should say that one of their principals a few years ago allegedly was in trouble with a US agency, but I have not had any problems with them.
I got 50 GB storage free, they still have that, subject to participation in some sort of achievements program.
Anyway just a thought.
Cheers all and Avagudweegend
Wizard