After much troubleshooting, I can at least confirm that on my Realme 8 Pro, my SD Card cannot be formatted to internal storage. I found an app that loads a shortcut to the Android stock file manager (Files by Mark Apps, i think), which has accessible settings to SD Card formatting. Internal storage formatting is disabled on the stock file manager.
It wouldn't be a stretch to consider that this could be the case for all future Realme phones.