I think V20 is still available for download
The issue is v20 has a launcher, so the launcher updates it to v21. Regardless, any version of Blockland (v20, is it?) that has the launcher to support it, it's just really a launcher. That is why the revisions are here instead of versions because v20, AKA Blockland Launcher just updates it all.
So unless it was hacked and made so v20 can launch without the launcher, v20 will go to v21.