I currently use TinyWall Firewall, it works very well, it’s small/portable, no complaints I even donated to the Dev but I would really prefer open source, also it needs to be user friendly like TinyWall so my non-tech family members can/will use it like they do with TinyWall.
There is a basic misunderstanding in OP’s formulation: a “firewall for” is something one needed with Windows XP and earlier, as in a piece of software that acted as a firewall; nowadays, both Windows 7+ and Linux come with a built-in firewall, that one might want a “GUI for {}'s firewall”.
Whether people feel more inclined to explain the misunderstanding, or to just spew a “you can’t” that’s technically correct but unhelpful… YMMV, different people are different and may be of different mood at different times 🤷