Since I’ve searched a simple yes or no to that question and could not find any I wanted to do this post to inform others.
There were little chances that it would have been incompatible on a hardware level since those kind of layers are managed at a system level and not that low-level nowadays. But still, I wanted to clarify that.
Yes exFAT is compatible with your hardware in fairphone3 and so most probably with fairPhone4. You only need a systemOS capable to handle it if fairphoneOS or android fork which is using fairphone cant handle it.
You also need to format it first on your PC.
I’m currently using a 512G (so no there is no size limitation in terms of card (again a misconception between hardware level and Filesystem level) EVO Plus. Formatted on one of my linux host with exFAT and MBR as partition scheme. Transferred the data from my old dying EVOplus. The phone directly recognized it.
I must add that my phone is under DivestOS(Faq - DivestOS Mobile) so not fairphoneOS or android per se.
So since it works there, it should work under lineageOS too and every recent fork of LineageOS. Most probably everything based on android 11.
Also little advice how to recognize a dying sdcard. When half full the card is not accepting any new files like it used too or any kind of strange behavior, just transfer your files onto your PC. try to “secure format” the sdcard (with dd if=/dev/random under linux) and look at the speed in real time or at the summary. If it’s very low compared to the theorical speed like 15MB where it should do at least 60MB (assuming you are using a relatively good sdcard reader of course) then yeah you can consider your sdcard as dying.