I had exactly the same issue. I installed Kubuntu (Ubuntu + KDE Plasma + Wayland) lts 26.04 and 70% of the time my pc would not should down cleanly. What I found out is that some specific changes to amd drivers were introduced in kernel 6.19 and onwards and are now being rolled back or fixed in 7.x. 7.x is not mature enough yet, even worse on ubuntu which lags behind with the kernel version.
It just so happens that 6.18 is a kernel that is lts and still receives fixes from ubuntu, so I manually installed the 6.18.48 from the ubuntu mainline, which is very stable and works very well with the newest linux-firmware.
I don’t think a kernel parameter is enough to fix it. I tried everything.