There'll be some way to make it work, possibly indeed that the Homebrew people get approved by Apple, because MacPorts works ok, and it seems to be downloading precompiled binaries (and if it isn't, then my Mac is actually faster than I've ever seen it run). And if MacPorts can do it, presumably Homebrew can do it too.
Building stuff yourself remains an option, even if you're unapproved. The toolchain pops the codesign step in at some point, I guess, and if you built it locally then you can run it locally. I just did cc -o on some bit of code on an Apple Silicon Mac, and the resulting binary did run.
(You can also run binaries that unapproved people built on other systems, but it's a minor pain, as you have to explicitly opt in to allowing each runnable file to run.)
MacPorts and Homebrew behave identically here: precompiled binaries are not affected, only .app (and similar) bundles.
(People find this confusing, because Homebrew does a superset of what MacPorts does: it distributes both source/binary packages and it distributes "casks", which are essentially a CLI-friendly version of the App Store and come with macOS's additional restrictions on applications. This only affects casks.)
The hierarchy is actually a little more complicated than this. MacPorts can and does build open source GUI apps (in fact it largely rejects binaries for them, preferring to build them directly). Homebrew rejects GUI apps from being built from source. Because Homebrew downloads apps from the internet, it makes them with the quarantine attribute, which means more apps that it handles will be flagged by Gatekeeper.
I see, thanks! Is cc installed by default? I remember when my ex-wife had a Mac she had to sign up for Apple's developer program to get compilers installed.
No idea what you get out of the box, or what /usr/bin/cc actually is and does, but it looks like the underlying compiler is the clang that came with Xcode, which I installed from the app store. I do have an Apple account, but I don't think it's signed up to Apple's developer program... at least, probably not? I'm not paying them for this, anyway.
Building stuff yourself remains an option, even if you're unapproved. The toolchain pops the codesign step in at some point, I guess, and if you built it locally then you can run it locally. I just did cc -o on some bit of code on an Apple Silicon Mac, and the resulting binary did run.
(You can also run binaries that unapproved people built on other systems, but it's a minor pain, as you have to explicitly opt in to allowing each runnable file to run.)