New macOS releases have historically led to unpleasant surprises. I'm running the beta on an older machine, so I'll post testing progress here. Most problems deserver their own issue. See #16387 for Catalina beta testing last year.

I consider Universal Apps out of scope for this issue.

I removed Homebrew and PyEnv first, installed Xcode 12 beta, before reinstalling them. This best represents what the actual OS will look like with a clean install. It also prevents Homebrew from installing Xcode 11 developer tools.

sudo xcode-select --switch /Applications/Xcode-beta.app/Contents/Developer

Beta 1

Build: 20A4299v on Intel CPU, using Xcode 12 beta (without Universal App support).

Downloading 0.20 binary from bitcoincore.org works fine (with right-click install).

Tested master @ 19612ca

I didn't test ZMQ and libmultiprocess yet.

Without depends

First I installed dependencies using homebrew 2.4.2. I use --build-from-source to see if there's any homebrew packages that probably need a Big Sure specific update . That revealed with a few problems.

Installing Python via PyEnv doesn't work yet (see pyenv/pyenv#1643), but you can install the binary for now, or via homebrew.

Brew can't install berkeley-db4 using --build-from-source, but it can use the Catalina bottle.

clang crashed for test/test_bitcoin-scheduler_tests; I sent a bug report to Apple, attached logs for @practicalswift and other compiler aficionados. I wasn't reproducible, not even after git clean -dfx.
crash.zip

With depends

I was unable to build QT the first time, but can't reproduce that problem. BDB may need a patch (#19411). During blockchain download catchup, I got a LevelDB read failure: Corruption: block checksum mismatch error. I'll see if I can reproduce that. See #19410.