how to change kernel boot parameters in systemd or refind

I am new to Linux and very confused. I need to change the i915.enable_psr and i915.enable_guc parameters or modules or whatever they are called to prevent my laptop from being in a constant state of agony, but I only recently found out that pop!_os instead of grub uses systemd or refind to boot or something and I genuinely can't find the alternative to the GRUB_CMDLINE_LINUX_DEFAULT from grub, can anyone help me? And could anyone be kind enough to tell me what the difference between systemd or refind is? Or one better, what do they even mean? P.S. In case it matters this whole ordeal started because of this: i915 Atomic update failure on pipe A And no, moving to a different os didn't solve the problem. Sincerely, One hell of a confused Linux noob.