Trying to fight spam with static filters is futile. Use the built-in junk mail controls instead, see https://support.mozilla.org/kb/thunderbird-and-junk-spam-messages

I find MANY spam emails per day in my Thunderbird JUNK file

So job done, what else do you need? You can tell Thunderbird to automatically delete messages in the Junk folder after a certain time, e.g. 14 days, if this is what you're after.

Thanks but I've tried all and more this many many times. All these spams from from different email addresses each time, all tiny tiny tiny countries overseas. I'm looking for a way to block any email address from little-known countries by whitelisting the normal and recognized .xxx codes and blocking anything else.

I'm looking for a way to block any email address from little-known countries

When 'blocking' means to move messages to Trash by a static filter defined in your Thunderbird installation, I don't see how this is fundamentally different from moving messages to Junk by Thunderbird junk mail controls.

It's unfortunate, but there is nothing you can do to prevent spammers to send you spam messages in the first place. And I don't think it matters from which country they come from.

If you want to block spam messages on the server, so that they don't even get to your local Thunderbird installation, you should talk to your email provider.

Something you can do is to keep your email address tight, and only give it to trusted correspondents.