David presented the following explanation :

This clear sealant seems to be set hard.
Moderate attempts with a knife won't cut it, and I am delaying getting
brutal because I don't want to damage the floor or kick board.

Some clear sealants can set very hard indeed, but why would they use it
on a kick board?

Kick boards used to be screwed in place, though later ones just clip
into place. All you can do is pull and cut until the board is free and
able to be cleaned up.

Mine are older ones, which screwed into place, fitted by me. I recently
re-did the floor, so all had to be removed, so I took the opportunity
to clean them up and repaint them all. Kick boards are quite cheap to
replace with new, if they are damaged.