How do I pass arguments from URL into panel page block?
I have not used Panels with D8, but...

With D7 Panels I remember there was a way to set/pass a contextual filter value, but one thing I noticed was if I did not set it in Panels and instead set it directly in the View's settings, it also worked.

So all you have to do is edit your View block, under Advanced, for contextual filters add Has taxonomy term ID



In the settings for that, select Provide default value and for type use Taxonomy term ID from URL





Alternatively, you could do