Black Lament The Anti-Cheat may be flawed in its sense of compatibility with the steam-deck. But you need to keep in mind, this is an in-house Anti-Cheat. They made it themselves, and it had came before the steam-deck was even remotely popular among the tech community. So there was never expectations for it to not be supported by HWID misconfiguration.
As disappointing as it is to not be able to play projects like this because of these reasons, it is within understanding since they are a very small team. When larger company's (ones like Larian-Studios, Take-Two, Pearl Abyss etc) even struggle with general Linux compatibility, I wouldn't imagine it to be a feasible task for Plutonium on-top of any roadmap they have most likely been planning out at the moment.
There has always been talk of supporting the steam-deck, maybe one day Eldor will flip a switch and decide to start working on the AC for compatibility, and maybe he never will. Regardless acting like this doesn't help, I personally wouldn't want to add support to a community that acts self entitled. No one in Plutonium is telling you to install a whole new OS to play, it is just simply that they are only able to guarantee (as said by Xerxes) support on the hardware they can test it on effectively. Also as he said, Wine is always changing, it's still missing A TON of Windows Calls, Hooks, userbehavior, not to mention general differences in user/sys space.