I did have the same exact questions about version selector but i think it's good to have an option to choose just in case you need an older version.
The public website and the CMS Kit, it's kinda related so i guess. you should keep it both in your project even if you don't need it, you can just publish one of them. I faced the same issue when i was trying the Blazor Server Version.
I found the solution. I just answered the same question in another ticket. I will post it here too. It's because there are some missing <Version></Version> tags in the **Volo.Abp.Account.Pro **projects.
Steps to solve
I had the same problem with the version 7.0.1.0. I found a workaround to solve this issue.
** <Version>6.0.2.0</Version>**
Check if all the Volo.Abp.Account.Pro.XXXX projects have the tag <Version></Version> inside of it.
I wanted to report this some weeks ago but i only few support count so i can't take a risk to report some bugs & solutions. I found 2 more related.
It seems to happen to Blazor but it works great with MVC (a note if you decide to switch to another UI)