Apparently Mint 20 is available for download

[buster]

While the upgrade procedure is not ready yet, the iso is. Supposedly the beta upgrades automatically to 20 final.

https://ftp.heanet.ie/mirrors/linuxmint.com/stable/20/

https://forums.linuxmint.com/viewtopic.php?f=90&t=322847

[fox]

I think it's going to be officially released on June 30. At any rate, I will be doing an upgrade, not a clean install. I have a few things that would be a pain to reinstall. So I'm waiting for the upgrade procedure, too.

The way I'll do it is to clone my 19.3 and install it on another partition. I'll then upgrade that and test it. If all is OK, I'll upgrade the partition I actually use. An yes, I realize that I can keep running 19.3 for several more years, but it's nice to have the latest and greatest stable release.

[Jason]

While the upgrade procedure is not ready yet, the iso is. Supposedly the beta upgrades automatically to 20 final.

That's the way they've done it in the past. That is, to let you upgrade the beta to the final. Really, it's just updating packages that probably have only changed a little bit from the beta to the final. It's most likely the same packages with fixes applied since betas are supposed to be feature complete.

[fox]

Mint 20 has now been officially released; you can get it from Mint's website. They mention there that the upgrade path will be released in July.