Hi,
in the dual pane view nemo shaded the whole inactive pane, including the
selected row, which kept its white "selected" foreground and became
unreadable - the effect in your screenshot. The rule only applies with
non-Mint themes, which is why it shows with Adwaita and friends.
It was fixed upstream in linuxmint/nemo#3261 by adding `:not(:selected)`
to the selector in nemo-style-fallback-mandatory.css. In Debian the fix
is in nemo since 5.8.5-2, so I am closing this bug; bullseye and
bookworm still carry the old rule and will not be changed for this.
I have also reassigned the bug from cinnamon to nemo, where the code lives.
Thanks for the report.