dippywood

So, here's the problem, and its resolution:
 
Comparing the decompiled DTBs for the SOPine for 21.02.1 and 21.02.3, diff gives me 
565d564 < non-removable; 600c599 < max-frequency = <0xbebc200>; --- > max-frequency = <0x8f0d180>; 681a681,682 > phys = <0x2d 0x00>; > phy-names = "usb"; 691a693,694 > phys = <0x2d 0x00>; > phy-names = "usb";  
Working through these show that only the first of these seems to make a difference. The definition for mmc@1c0f000 no longer contained the 'non-removable' entry. 
 
Therefore, inserting "non-removable;" at line 565 of sun50i-a64-sopine-baseboard.dts and compiling to /boot/dtb/allwinner/sun50i-a64-sopine-baseboard.dtb resolves this issue.
 
I can supply a patched focal image if requested.
 
 

@SecT0uchIf you are able to mount the image on another system then you could make the update in place
 
Something along the lines of (adjust paths to suit your setup)
mkdir /tmp/image mount -v -o offset=4194304 -t ext4 /Path/To/Armbian_21.02.3_Pine64so_focal_current_5.10.21.img /tmp/image dtc -O dtb -o /tmp/image/boot/allwinner/dtb/sun50i-a64-sopine-baseboard.dtb -b 0 sun50i-a64-sopine-baseboard.dts umount /tmp/image  
Then write the image as usual
 
You can mount this from another Linux system. from WSL2 or whatever, as long as you have the dtc command avaialble. 

In my stupidity when renaming my temporary files I used the wrong extension - the file previously attached is the DTS.
 
So, here it is, with the proper extension.
 
I have asked for a new brain for my birthday! 
sun50i-a64-sopine-baseboard.dts

So, here's the problem, and its resolution:
 
Comparing the decompiled DTBs for the SOPine for 21.02.1 and 21.02.3, diff gives me 
565d564 < non-removable; 600c599 < max-frequency = <0xbebc200>; --- > max-frequency = <0x8f0d180>; 681a681,682 > phys = <0x2d 0x00>; > phy-names = "usb"; 691a693,694 > phys = <0x2d 0x00>; > phy-names = "usb";  
Working through these show that only the first of these seems to make a difference. The definition for mmc@1c0f000 no longer contained the 'non-removable' entry. 
 
Therefore, inserting "non-removable;" at line 565 of sun50i-a64-sopine-baseboard.dts and compiling to /boot/dtb/allwinner/sun50i-a64-sopine-baseboard.dtb resolves this issue.
 
I can supply a patched focal image if requested.
 
 

@IgorPlease do not think that your efforts are unappreciated - they are, and greatly so. I was simply concerned that the board status was not what I expected. 
 
I also agree with the work-around - and thus me taking the builds and working out which would work for @robocone
 
I am also not adverse to providing workarounds when I can, and, as time allows, I will attempt to identify exactly where the problem is, and share same.
 
Once more, the efforts here are greatly appreciated (at least by myself) and I remain grateful for all of your efforts. If I can find the cause then I shall do so, but. for me. the 'free' is very valuable
 

@IgorPlease do not think that your efforts are unappreciated - they are, and greatly so. I was simply concerned that the board status was not what I expected. 
 
I also agree with the work-around - and thus me taking the builds and working out which would work for @robocone
 
I am also not adverse to providing workarounds when I can, and, as time allows, I will attempt to identify exactly where the problem is, and share same.
 
Once more, the efforts here are greatly appreciated (at least by myself) and I remain grateful for all of your efforts. If I can find the cause then I shall do so, but. for me. the 'free' is very valuable
 

@IgorPlease do not think that your efforts are unappreciated - they are, and greatly so. I was simply concerned that the board status was not what I expected. 
 
I also agree with the work-around - and thus me taking the builds and working out which would work for @robocone
 
I am also not adverse to providing workarounds when I can, and, as time allows, I will attempt to identify exactly where the problem is, and share same.
 
Once more, the efforts here are greatly appreciated (at least by myself) and I remain grateful for all of your efforts. If I can find the cause then I shall do so, but. for me. the 'free' is very valuable