I use the latest plain Big Sur 11.2.3 version coming via software update / App Store - nothing fancy and no pre-releases.
Yes, it's better not to use Beta releases, but my PC is with latest betas since long time and didn't want to spent time on this.
And for the next post - yes - most probably it was command line tools - Xcode is very picky at this point - especially if you freshly installed Xcode and never accepted the "user agreement" even the command line tools won't work properly.
This is good to know. I didn't know at all that Lazarus has something to do with the xcode and command line tools.
Now, I'll keep in mind that I have to keep an eye on these tools as well.
And still don't know why exactly Lazarus needs the command line tools. I assume it is only for development and later when I prepare the installation for my clients it won't be necessary. But I'm far from that.
May be, FpcUpDeluxe could somehow catch such situations and show some message pointing in the right direction.
(don't know how much useful is this, but just to share my thoughts and ideas)