I don't have Canada, Mexico like that many choises. I only have Argentina.Australia.Germany.Japan.South Africa.United States in my vpn

Yes there are not that many choices:

Search the forum to see more about this

example:

https://support.mozilla.org/en-US/questions/1575487

Hello

https://support.mozilla.org/en-US/questions/1602367

The built-in VPN is not a full VPN but rather it routes your browsing traffic through a proxy network that replaces your IP address before it reaches a website. The sites you visit see the proxy’s IP address rather than your own. Unless otherwise most free built-in or browser extension VPN's route browser traffic through proxy servers and is not a full VPN like the standalone subscription based Mozilla VPN apps are.

With more users and because it is free perhaps some locations are not always available for some. Mozilla just did finish with a unlimited data usage promotion between June 9th and August 31st.