I forget. Did they remove the little plastic square thing to make it read-only?
For youngins, 3.5" floppies had a "write protect" switch. If it was a solid plastic bit, you could write, but if the switch showed a hole, it would be treated as read only. Here's the first Google result I found: https://electronicstechnician.tpub.com/14091/css/Write-Prote...