IONOS also provides CalDAV hosting, even just with their "Mail Basic" plan.
To configure a calendar client (like Fantastical), you just need the CalDAV URL, which can be found here:
Added as account to Fantastical:
Any device, anywhere
New device, no hassle
Serious about privacy
Read some challenges to be expected with Apple devices.
Most importantly, tried to sign up to test but got an error: