We're reaching the end of an era wherein billions of dollars of investor money was shovelled into tech startups to build large user-bases, and now those companies (now monoliths) are beginning to constrict their user-bases and squeeze for every single penny they can possibly extract. Fair or not.
Now more than ever, it's important for us to step back and reconsider whether we want to be billboards for these companies anymore.
For anyone unfamiliar, some good resources to have when starting your degoogling journey are below:
Privacy Guides - A list of privacy-respecting services you can use.
Plexus - A crowdsourced information bank of service compatibility with degoogled devices.
This random PDF - A study from 2018 detailing data that Google tracks about its' users.
I use nextcloud for calendar (among other things). I made an account for my wife on the nextcloud and we share a "Family" calendar on there. It's also possible to share publicly with anybody, but they can't create or edit without an account. Of course, it's more work to set up. There are also alternatives like zoho, etc which might be easier to get started with, but I haven't really tried any of them in years. I don't know how many people you share with, but if it's not too many, there might be options. I don't have to host my own nextcloud. I have mail service with my personal domain through mxroute.com and it includes Nextcloud.