Card reader mode works here, its just a tiny bit slow.
One issue, that I have pointed out a few times, is that Axoloti creates patch folders in the root of the SD-card, which slows down the load time a lot, especially if you use the card read mode. So basically every patch you make, there will be created a patch in the root folder. This will sum up. I have sometimes had to clean out hundreds of patch folder at a time to keep the load times reasonable.
I think it would be SUPER great if we as users were allowed to be able to set a "patch folder" in preferences, where all the patches are placed in, instead of all being placed in the root, it just creates a mess and makes loading sd-card in card read mode a lot slower.
The read only sd-card part, there is a small slider on the side of the sd-card, which sets if an sd-card is read/write or read only. Be aware that it can be a bit hard to set it right, sometimes the slider doesnt even have to be in one or the other side, sometimes in the middle...... So Try on the computer where you know it works, to get the sllider placed so you can write to it again and then put it back into axo.