Native exFAT is now a thing on Android 13 for Pixel devices: https://blog.esper.io/android-dessert-bites-27-exfat-on-pixel-532176849/
The upstream exFAT driver is used so older kernels can't support it, that's why it's only working for 6th generation Pixel devices (and future devices). Android 13 finally added userspace tools to make that work.
Now that GrapheneOS has been ported to AOSP 13, how's your experience with exFAT? Does that work for you? Sadly, none of my two exFAT hard drives seem supported. They were formatted in macOS so I'm especially interested to hear from users with exFAT drives formatted by macOS.
Feel free to share your experience with native exFAT support nonetheless!