Regularly cleaning fluff and dust is generally good advise to keep the system as cool as possible.
In case of a general heat issue - re-pasting critical components (cpu and gpu) may also be good advise.
I don’t think this is the issue here because
Compared to Manjaro Linux, Ubuntu Linux generally uses older kernel
So the topics below may be worth checking
Udev rule to lower AMD CPU 'scaling_min_freq' value for kernel 6.13 & up