Error backend subprocess builder python3.11-pyqt6-6.7.0 - general "stability" questions & howto?

[DocPBrain]

Sorry in advance, I don’t know what I’m doing.

Question1
I’ve been trying to slowly figure out nixos on a secondary machine running nixos-unstable channel for about a year now. I definitely have always preferred a rolling release, but it seems like about 15% of the time I run “nixos-rebuild switch --upgrade” I end up with a problem (like Question2 below) which I may or may not figure out, but if I don’t, I just end up having to not use the package I wanted to (remove it from configuration.nix).

Why is there no rolling `stable` channel?

I’ve always used nixpkgs-unstable but am considering dropping back to a stable channel now, particularly when pinning nixpkgs in individual projects. I’m surprised there’s no nixpkgs-stable though - I would expect this to just point to “the latest stable release channel” (i.e. 19.03 right now, but pointing to 19.09 once that’s released). That way you get stability, but when a stable release is made you get that upgrade by default, rather than having to upgrade release branches everywhere you’ve …

I read the above thread and saw the mention of using multiple mixed channels but I’m not sure if I should try to figure out how to do that or just switch to stable/non rolling channel. Advice please?

Question2
My current actual issue is “nixos-rebuild switch --upgrade” won’t complete and it doesn’t seem to be due to a particular package as it has been frequently before.
If I need to provide more info, a log etc, please let me know.

ERROR Backend subprocess exited when trying to invoke build_wheel
error: builder for ‘/nix/store/8b01w19ymf8w9grnbsr7vhd1vccgxax2-python3.11-pyqt6-6.7.0.dev2404081550.drv’ failed with exit code 1
error: 1 dependencies of derivation ‘/nix/store/xrdpcsb2c9csyz2l1z7lviwd3h7zyrkp-python3.11-pyqtgraph-0.13.7.drv’ failed to build
error: 1 dependencies of derivation ‘/nix/store/wj3161c5sbsa9p1q4vjc8k8nj5s0z3n9-tribler-7.14.0.drv’ failed to build
error: 1 dependencies of derivation ‘/nix/store/rhlbc7lvdp3ziwvdp3p9n399b4gd2wj5-system-path.drv’ failed to build
error: 1 dependencies of derivation ‘/nix/store/c175asxw87jx8dnmysgvnpf31sqjmyc0-nixos-system-x270-24.11pre692963.a3c0b3b21515.drv’ failed to build

[DocPBrain]

After a half dozen attempts and ~48 hours, I was able to find the combination of packages which were causing the build errors, thus working around Question2. I am, however, not at all content with this method of doing things.