At such times tend towards whipping out the big guns "sudo systemctl mask". Though helps to nose around a bit to see if there's affected dependency issues, often not. I like to nuke NetworkManager in this fashion. Someone can blacklist modules in /etc/modprobe.d files, so they don't load, should already be some examples there for cpu microcode, one per line etc. Have also seen the weirdness with kernel parameters not taking effect when added to /etc/default/grub as they should, tend to just keep poking at it, put it down to syntax or ordering error.
As Head_on mentions cat'ing /proc/cmdline to check. At times will do this via the grub screen, highlight the kernel line someone wishes to affect, press the "e" key for edit, add the params you're wanting to it and go from there, although don't believe it's meant to be persistent(only for that boot) and the grub file is where such things are supposed to be done. There's a second line in the grub file below the first, related to adding params, seems setting them there remain in effect vs using the first one. Really haven't sorted out how this works in detail. Just poke at it when needed, until output of "cat /proc/cmdline" shows me it's working as I'd wanted it.