Marco Schirrmeister

I would go with, like you wrote, ext4 or xfs. If something breaks, you can still mount the disk on any other linux system without any issue.
Ext4 should also not have any problems with big file sizes. I am running xfs without any problems since years. Even if there was a hard crash, the filesystem could easily be mounted since nothing really happened on it or the recovery was smooth.
 
I would probabyl still argue that ext4 is even more robust. For a simple disk to store some data it might still be the best choise.

I have no idea what this rk3588-sata2 overlay is supposed to do. But I don't think you need it.
For you adapter, I guess you have one of this M.2 to sata adapters like this? https://www.amazon.de/gp/product/B0B6RQHY4F
I am pretty sure I tried to use this adapter directly some time ago and it was visible too. But that was the classic Orange Pi 5.
 
In lspci, you should see something like this.
05:00.0 SATA controller: ASMedia Technology Inc. ASM1166 Serial ATA Controller (rev 02)  
Try to load the edge kernel 6.7 image. That one has received a lot of hardware support for the rk3588.
All what it needs is the ahci driver.
 
I do something similar on my OPi5+.
I have a M.2 to PCIe riser card. In there is a pcie switch card with a ASM2812 chip. This card has 2 M.2 slots. In there are M.2 to SATA3 adapters with an ASM1166 chip (each 6 ports).