Perhaps secure boot by itself isn't enough, but I would imagine it would be a relatively large bump, when combined with a kernel-level anti-cheat. I presume such anti-cheats would e.g. disable the debugger access of game memory or otherwise debugging it, accessing the screen contents of the game or sending it artificial inputs.
What vectors remain? I guess at least finding bugs in the game, network traffic analysis, attempting MitM, capturing or even modifying actual data in the DRAM chips, using USB devices controlled by an external device that sees the game via a camera or HDMI capture.. All these can be plugged or require big efforts to make use of.
VALORANT also adds TPM to the mix alongside SB and a kernel AC and yet is still trivially easy to cheat in as long as you have a driver you can use. Granted, it needs to be signed (=financially unreachable by a big part of the community), but if stubborn enough...