According to the new regulation of Government in Poland on restrictions related to COVID19 , published on 26 February 2021, among others, new measures also were introduced regarding rules for traffic from Czech Republic and Slovakia to Poland.
However the provisions foresee that drivers engaged in road transport, as part of international road transport or international combined transport within the meaning of the provisions of the Road Transport Act, are exempted from quarantine and the obligation to present at entry to Poland a certificate confirming negative COVID19 test results.
Exemptions to these obligations include, drivers performing road transport as part of international road transport or international combined transport within the meaning of the provisions on road transport, returning from abroad or passing through the territory of the Republic of Poland in transit by means of transport other than the vehicle used for road transport:
a) in order to take a rest in the territory of the Republic of Poland or another country,
b) after taking a rest abroad.
Information about it on Polish Border Guard site here.