I know you're asking for free but have a look at the paid ones on certain dates (as in holidays/deals/etc.)

I got my NordVPN Black Friday deal which costs 99 buckeroos for three years which comes down to just 2.75 bucks a month. Yeah it's not free but 2-3 bucks a month for privacy, watching NF unrestricted, etc. is no money in my opinion.

There's also a solid guide on how to set it up under Linux Mint in their knowledge base.

(also do your research about VPN providers first, I trust NordVPN because they claim to be based in Panama among other things but you might not)