Grails developer / build calendar with recurring events

We are looking for an experienced grails developer to work on one of our clients projects. They are currently working on updating grails from 3.2.6 to 5. Apart from that they need help with building a calendar logic with recurring events. The work would definitely be longer term, as you would be working with alongside an already existing team.

Tech stack:
Grails
PostgreSQL
Heroku
AWS
S3
(Lambdas)
Git / GitHub

Special know-how:
If you have implemented recurring calendar events, that's a plus :)