It is not a stretch that such RF exposure could potentially have carcinogenic properties, but that needs context, the likelihood of a cell phone is pretty much nil.
That’s not how non-ionizing radiation works. The MPE exposure limits are because you can be effectively cooked, not because you’ll get cancer. You need much more energy to do that, like UV light, X or gamma rays.
The easiest way off the top of my head would be reinstall and manually design your partitioning so anything that’d benefit is on the SSD and everything else is on the HDD. You might be able to get away with
/
on the SSD and/home
on the HDD, I don’t know what all you have installed or what amount of space Ubuntu requires by default. If you wanna go this route, I’d start your reading here: https://wiki.archlinux.org/title/Partitioning#Partition_scheme