Here are links to sources of information you should check if you are planning to visit Santiago de Compostela or Galicia, especially from abroad:
Health control process for travellers visiting Spain:
+ INFO: Spain Travel Health
Resolution of 4 June 2021 of the Directorate-General for Public Health on health checks to be carried out at points of entry into Spain
Measures and information that travellers visiting Galicia should be aware of.
+INFO: Turismo de Galicia