Make Debian automount mount devices in read only

[Carles Pina i Estany <carles@pina.cat>]

Hi,

My desktop computer (Debian 11.2) auto-mounts USB devices (hard disks,
etc.)

I would like the devices to be mounted in read only mode by default. I
will remount them in rw if I need to.

They are not in my /etc/fstab

I've been looking at udev configuration files, rules, etc. but I'm
unsure which is the best way to go.

Is anyone here a bit more familiar with udev, systemd, etc. let me know
of a good approach please? The current Debian (and for many versions)
worked so well for me that I haven't dealt with this kind of settings,
I don't know which is the right tool to setup or how they interact with
eachother in detail anymore :-)

Thank you!

-- 
Carles Pina i Estany
https://carles.pina.cat