The Czech government decided today that from tomorrow, May 26th, there will be no continuous border controls at the borders with Germany and Austria, only random checks. However, the general restrictions for entering Czechia remain, i.e. the requirement for a negative corona test and a good reason to travel (you can find more information here).
There are also some Eurocity trains running between Berlin and Prague. The traffic will be expanded in June. The Nationalparkbahn/U28 does not yet run cross-border again.