I especially enjoyed how relatively open Uplink was. Putting other hackers behind bars through International Crime Database, stealing millions of dollars from an account where a "trace a huge payment" contract ended up - things like these shaped up my love for open world games, and immersive sims alike.
My tailnet is set up using a GitHub organization, without using Google at all. I have sufficient security (2FA with security keys, etc.) enforced for it. I think that hand-rolling their own auth would not be a great idea just yet, while they are still ironing out other features.
There are more options than that, and I see your point.
To take the contrarian stance though: SSO not being paid is kinda nice, and not having yet another password for something is nice. —- double and: then not being able to leak a password or handle 2FA, instead focusing on their actual product.
For free users, it's pretty much just G, MS, and GH (which is currently the only "tolerable" one, but there's no reason why it won't turn into a MS account in the future just like how they killed Minecraft)
You can use Nix (https://nixos.org/nix) to install these tools on any Mac/Linux machine (nix profile install nixpkgs#{bat, delta}). Disclaimer: I packaged some of these tools for Nix :)