-------- Original Message --------

> There aren't many filesystems with rw access on both Linux and OpenBSD
> (IIUC FFSv2 is ro on Linux if it works at all) and of the ones which do
> exist, this is a lot more unix-ish than FAT32...

Assuming newfs always creates ffs2 these days even on a 1G fob then it works
with mount -t ufs -o ufstype=ufs2,ro. On Devuan (Debian 13/Trixie) it says
compiled with read-only support. The man page says "used in FreeBSD 5.x
supported as read-write" but not sure if I would trust it even if it had worked.

I find exfat from packages/ports works across OpenBSD, Linux, Android, Windows
and I believe Apple devices. It has some naming quirks but is generally okay.
Quite slow on OpenBSD though.

-- 
All the best,
             Kevin Chadwick