Here's the issue re. FAT formatted drives:
For Audacity 3.x, a new single file project format was developed.
Why? Because it is heartbreaking to see inexperienced or less technical Audacity users permanently losing their work because they haven't understood the concept of a multi-file project format. Week after week on this forum we would see users that had inadvertently destroyed their own work, sometimes valuable, never to be repeated recordings. In one sad case it was the final words of a relative.
The technical challenge: how to modify data in the middle of a long track without having to write the entire track data (which could be several gigabytes).
The original solution was to split the track data into small "block files" (the ".au" files in the _data folder), but how to do that with a single file format? It is not possible to just write data in the middle of a normal computer file.
The answer was to use a kind of database - SQLite
As with other databases, it is possible to access chunks of data, read them, modify them and write them back to disk. Unlike other databases, SQLite manages to achieve this yet still use a single file format for the database.
After many years of thinking, discussing, and considering very many possible solutions, SQLite looked like the best answer. Two of top developers began working on developing a "Unitary Project Format", based on the SQLite database.
Unfortunately, a snag was discovered:
One one of the platforms that Audacity supports, there is an ancient (44 years old, which is an aeon in computer technology) disk format called FAT, which is still used today. By today's standards, the FAT file system and is very primitive. Among it's many limitations, it does not support file locking, which is required by SQLite in order to perform secure transactions.
There were two choices; either abandon the work, or drop support for FAT. An executive decision was made to drop support for FAT. In this case it was decided that the needs of the many outweighed the needs of the few.
Since Audacity 3.x has been available, the number of cases that we've seen on this forum, of people losing / destroying their projects, has reduced very noticeably. Of the few cases that we have seen recently, most if not all have been using older (2.4.2 or earlier) versions of Audacity, with the old "pile of files" project format.