Even when ´they were what they once were´ these trains (just a part of the train that arr. in Plzen HN, and NO cars with REServ chances) were not up to the standard of the prime INTern expresses (and express they also never were). But the only other 2 more or less direct border crossings from CZ into Bayern=Bavaria is the above most northern and once the main ´go into the communist world´ via Cheb-Schirnding is for this relation much time consuming-probably even without direct ticket availability, as its a detour, or #2: with many changes and tiny local trains via Zelezna Ruda, its quite some time ago since I last did this way, but I expect the standard as such to be even less as these direct trains-unless you are a dedicated branch-lines lover or the like.
The most common complaint about this link seems to be -for whatever reason (sometimes also stringent border checks at the german side)- missing the ´connection/shunting´ into the München train-forcing you to wait for the next one.
IF you have some kind of InterRail-pass or so: via Austria-Linz, but this will also eat time and is more fit if one stays (Cesky Krumlov!) in the south of Czechia.
Beg me pardon to suggest the better ALT; a direct BUS-like FLIX or the like.