Currently if you try to list 2.0.0-beta.1 as the minimum supported gateway version for an add-on in its manifest, the "Check changes" GitHub Action on this repo will fail because it doesn't recognise that as a valid version number according to the JSON schema.
Because the addon-proxy filters out 2.0.0-beta.1 as being older than 2.0.0 you can't just list 2.0.0 as the minimum version, so you have to list something older like 1.0.0 which might not be accurate.
Came across this problem with the Zigbee and X10-CM11 add-ons.