In brief, coronaviruses make all their proteins as one long chain and then cut it up into the appropriate pieces to form the proteins (spike etc). 3CL protease is the cutting machine and Paxlovid inhibits that.
The UK scientific advisory group SAGE published a few months ago that combination therapy might be useful to avoid 'antiviral resistant' strains of SARS cov-2 evolving. Perhaps these 3cl protease inhibitors may be used in combination.