I had the same "permission denied" problem (MBP2019-Intel, plus an older Intel-based machine plugging it into a USB port using a converter) and tried all the suggestions above with no improvement. I was using the built-in MicroCard port of a UGreen brand thunderbolt port expander.  (Also tried several Linux VMs, in Parallels and VirtualBox, on the same machines.) The thunderbolt port expander does correctly read/write ordinary files on MicroSD cards.

Then I tried plugging an **older UGreen USB-based card reader into the UGreen thunderbolt gizmo**.  **That worked** on the MBP; it's blazingly slow.  

I've previously been disappointed with other UGreen devices, but all the low-end options look like they use the same boards with different casings for branding.  They all get crappy ratings.  (Hint: don't use the charging port if you can avoid it.) I'm not convinced the more expensive ones would be any better, but maybe I'm too pessimistic.