Hello. Thanks in advance for the suggestions. I'm going to go for the easiest option for now, which is to buy a new nvme drive, Nvme 250Gb Kingston Nv2, which according to a listing on the radxam forum works fine. Also, according to the same list, the HP EX900 doesn't work directly, and it's the one I'm using. And in the images of balbes the disk is recognized, so I thought it would work, but no.
For now I am left with the complete UART register, because according to the little that I was looking at on the web, it is not something easy to implement. It is not putting a command in the terminal and that's it. And I'm short of time to implement it right now.
I hope I can fix it with the new drive. The truth is that I've had the board for several months and I couldn't make any progress at all because of this nvme and font compatibility issue. I already had to buy a source, even though I had bought the official 30w source, which was what Radxa recommended. And continue the party. Thanks again..