How to encrypt Dropbox subfolder so it can also be synced on Windows?

I have installed Dropbox on Zorin 17.1 and it seems to be working fine. However, I want to add a subfolder within that dropbox folder and encrypt all files that go into it. I am also syncing dropbox to a Windows PC (and another linux machine) and need the files to be available on all of them.

Is there a way to achieve this?

There is Cryptomator, you might want to check it out and see if it suits your needs. This thread may be a bit out of date, so make sure to contrast it with the official documentation.

Thanks I'll check it out.

This seems to work well. However, the only issue I have with it is that I can't work out how to get it to startup when I login. Having to start it manually is slightly frustrating.

I'm not sure how to do this either, I've never tried to set it up this way.

The only reference I found that can be useful is using one of their plugins to use KeePassXC as a backend for your passwords. It looks good; once setup, it should decrypt automatically the vault you are trying to access. But I suppose KeePassXC needs to be running already with an unencrypted database.

KeePassXC is a password manager, btw. If you already use it then it won't be an additional step in your setup.