I saw a post on the Steam forums that a public beta is available on both Steam and GOG but I don't see downloads for anything other than 1.0.28324 which I already have.

Do I have to do something to opt in to seeing beta versions?

For Galaxy users:
https://support.gog.com/hc/en-us/articles/360003904358-How-can-I-access-beta-channels?product=gog

For Heroic and Lutris on native version there is no option for this that I can see, I checked.
But if u run the wine version I think it might work, it looks like in the pic for me when ur initially installing it.

On Lutris I dont see an option for it on either native or wine version but I could be wrong and there is another workaround.

So if ur like me and use Linux and dont use the galaxy wine version we are just gonna have to wait a bit xtra :)