#lmde7 does not automatically mount ext4 (and ext2 and ext3) filesystems. The issue was reported
https://github.com/linuxmint/lmde7-beta/issues/20
but closed because of the new udev rules from #trixie (debian 13) on which #lmde7 is based.
I'll remove the rule from udev and see what happens. I guess it will work as reportedly other (virusfree?🤔) filesystems like exfat, fat32 etc. will be automatically mounted. No, it is not just the settings in #nemo
Of course, virtualbox was removed during the upgrade and the kernel was downgraded from 6.12 to 6.1 prior to the real upgrade and later installed, again.
I had to use the 6.12 kernel version for support of my #wlan chipset.

usb-stick mount: no automatic mount of usb-device formatted with ext4 · Issue #20 · linuxmint/lmde7-beta
usb memory device with ext4: after inserting, the usb device will not be mounted and nemo file manager does not open automatically. I have to go manually to nemo and "device" section. There I will ...