This is similar to Fairphone’s situation. For the Fairphone 5 they just use an IoT chip with long term support from Qualcomm enabling them to give at least 5 years of feature updates and 8 years of security patches.

Nix is a big rabbit hole. You can use it as a normal package manager, but there’s a lot more.

You can also use nix-shell to temporarily install packages, it drops you into a shell with your package and that package is gone when you exit the shell. You can also declare a shell using a shell.nix file with environment variables and packages you want (including specific versions) and enter that shell by running nix-shell.

You can also declare your full user environment using nix home manager. Using a home.nix file you can list packages you need and configure everything. That also makes it easy to backup your user environment by just copying the home.nix file.

The GT 730 is a very low power GPU, it is even slower than many newer integrated graphics. I’m assuming you mean you have an i5 12400 CPU since you also have DDR5 RAM, which is a good CPU on a modern platform. You should really upgrade you GPU and maybe also upgrade to 16GB RAM as many games require 16GB and having 2 sticks of memory also improves performance by running in dual channel.

I don’t think it’s on Homebrew, but it is available on Nix. Nix has a much bigger repository comparable to the AUR and you can use it as a normal package manager.

Other people have already said this in other comments on other posts, but in short Manjaro breaks easier than Arch because it ships stable older packages, but combines it with unstable new packages. The AUR can easily break on Manjaro, and ironically the same is true in reverse. Manjaro has broken the AUR before and they’ve let the SSL certificates expire, multiple times. The devs even suggested users to change their system clock back as a temporary fix. You’d probably be better off learning Arch itself or use Endeavor OS, although I personally haven’t tried it.