Hi, I have an Iphone pro 12, an Ipad pro 2nd generation, both have the same problems, On my desktop I have Teams version 1.4.00.4167 and on my apple devices the latest download (2 days ago).
I would start troubleshooting AAD Conditional Access policies that might block loading Exchange calendars on a mobile device/unenrolled device/non-compliant device/etc. Your Teams calendar is loaded by Exchange (each team has its own mailbox, etc.) and your PC can see them!