Delta, United, and Lufthansa have round-trip flights from Portland (PDX) to Split or Dubrovnik (SPU, DBV) for $528-$551 with multiple connections. Flights July to August. 7-day minimum stay required.
Croatia is reopen to tourism. Travelers need proof of paid-in-advance accommodations, and either proof of vaccination or a negative COVID test for entry. Fill out form on Croatian web-portal before arriving.