I personally usually go to older versions from the official beta RSS feed: <![CDATA[Latest Unity Beta Releases]]> but you’d need some RSS reader for this (I just use a browser extension for this).
I’m assuming the reason we don’t see betas and alphas on the regular archive is because Unity wants to keep preview stuff separate. Basically every alpha and beta does have such individual archive page, for example you can find separate archive for 2020.1 betas and alphas.
Well if both Alpha and Beta are available from the Unity HUB on the same page you can download official release, that wouldn’t make any sense. Not even a different install page, its right down, 1cm below.
There is a quote with the link to the archive for official release, then why not adding a single line to the top for the alpha and beta lines with the archive url anyway…
Just saying…
Well if I do so, it started to crash error related to the inapp purchase package.
Now everything runs fine with a16/17. no error logged, then XR + in app purchase are doing what they can do the best.