Gonna leave it here because someone might find it useful and my googling didn't come up with the answers that I liked.

So. I successfully switched my TerraMaster D2-310 from RAID1 to SINGLE mode, where each physical drive corresponds to a distinct logical one. Despite multiple sources stating that such a switch requires wiping the drives, I found a method that worked for me. Keep in mind that results may vary, and this might not apply to all enclosures.

Here are the steps:

1. Power down the enclosure, disconnect it from your PC, and remove Drive 2 from the enclosure.

2. Connect Drive 2 to your PC motherboard using a SATA cable.

3. Turn on your PC and ensure Drive 2 functions properly, allowing you to read and write data.

4. With the enclosure powered off, switch the MODE setting on the back of the device to SINGLE mode. WARNING: Do not, DO NOT press the Reset button, as it will most likely wipe your drive!

5. Power on the enclosure with Drive 1 inside and connect it to the same PC where Drive 2 is already connected.

6. Windows cannot mount Drive 1 due to its signature matching that of Drive 2, which is desired.

7. Open Disk Management, locate your "Offline Disk," right-click on it, and select "Online." This action changes the signature of Drive 1, effectively removing it from RAID.

8. You can now navigate to the root of each disk and delete any hidden folders containing RAID information. I removed the 2 folders starting with a "." (dot).

That's it. Aside from other obvious benefits of NOT having to tie 2 drives together, I believe I will get better longevity of my second drive now because I will use it to back up only the important stuff once a day.