There haven't been any substantial changes to the entry rules, so generally speaking, as long as you are fully vaccinated you can still enter the country for any reason - you will need to complete the Einreiseanmeldung and upload your proof of vaccination in advance:
https://uk.diplo.de/uk-en/02/coronav...330826-0-panel
I don't know about the local rules in FRA regarding restrictions on hotels, restaurants etc. but your hotel will able to advise.