Although the SDXC standard formatting is exFAT (and SDHC is FAT32 etc), I have never seen a problem with using a different file system - except the issue with portability that the OP has.
Of course, that's just my experience. But you'd think any problems would show up among the myriad of people who use SD cards for Raspberry Pis (and other things - like the PinePhone). Also, any performance issues would show up in tests like these that use hdparm, dd, and iozone. Those tools certainly doesn't use any of the FAT file systems, or even partitions; in fact they do raw reads and writes to the device.
As long as you have a sane operating system that doesn't start to "repair" a disk without you asking for it, there should be no problem moving a boot hard drive from one machine to another for data transfer. (Trying to boot from it in another machine may be another matter, but that's not what we're talking about here. And even this often works just fine with e.g. Ubuntu.)
In short, I think you've been fooled by FUD (and experiences with bad OS:es?), and you are spreading it further. One should always backup one's data. Do that, and then use the hardware you bought to its full potential.
Anyway, I hope the OP has gotten an understanding of the issue with the small capacity by now.
Of course, that's just my experience. But you'd think any problems would show up among the myriad of people who use SD cards for Raspberry Pis (and other things - like the PinePhone). Also, any performance issues would show up in tests like these that use hdparm, dd, and iozone. Those tools certainly doesn't use any of the FAT file systems, or even partitions; in fact they do raw reads and writes to the device.
As long as you have a sane operating system that doesn't start to "repair" a disk without you asking for it, there should be no problem moving a boot hard drive from one machine to another for data transfer. (Trying to boot from it in another machine may be another matter, but that's not what we're talking about here. And even this often works just fine with e.g. Ubuntu.)
In short, I think you've been fooled by FUD (and experiences with bad OS:es?), and you are spreading it further. One should always backup one's data. Do that, and then use the hardware you bought to its full potential.
Anyway, I hope the OP has gotten an understanding of the issue with the small capacity by now.