Thanks. I'm on MIUI Global 10.3.6 and want to use a Samsung 128 GB microSD factory-formated as exFAT. So I will try.
I'm on MIUI 11 now and use a Samsung 256GB SD Card, exFAT of course, no problem at all. I installed it on my phone right after taking it out of its packaging, it works, it's already formatted.
But from experience, some custom kernels can have a problem with this. So I took it out again and formatted manually on my PC as exFAT of course, before putting it back in, no kernel problems.
P.S. I also used 128GB exFAT when I was in MIUI 10, no problem ... Same on my Pocophones, all good.
Using Morfuz 3.4 kernel on my Note 7, Franco Kernel on my Pocophones