[devanl]

In case you haven't seen the UF2 file format, it's specifically designed to be robust w.r.t ensuring that the content makes it to the target intact despite common OS quirks.

https://github.com/microsoft/uf2

  - Data is divided into 512 byte blocks, which lines up with the mass storage transfer size.
  - Each block has an identifying magic sequence, a payload address, and size, which can be used to identify the destination.
    - This allows the emulated storage to ignore metadata blocks and to handle out-of-order and repeated blocks.

[catiopatio]

The UF2 format is a hack that can be made to generally work (e.g. it relies on things like per-block beginning and ending magic numbers to identify blocks that should be written to flash, which means isn't dependent on seeing FAT table writes in a particular order).

UF2 is just the file format, though. The mechanism for reading/writing UF2 files is via the emulated USB mass storage, which is fundamentally broken.

The USB storage device responds to SCSI write commands with a success status, but actually throws away data, such that a successive read does not return the previously written blocks.

To an OS or filesystem, that's just a failing drive. You might get lucky and things might work.