Hello takoyaqii,
Welcome to the Microsoft community.
I have received your reply here. I would like to confirm with you that you are using Excel online and there are no Year, Month and Quarter fields in the pivot table panel? Feel free to correct me if my understanding is wrong.
I have also tested this side of the synchronization, and there is indeed a situation that you encountered. Your understanding is correct, Excel online is lighter than the client and some features are not yet perfect. If you want to use these features, we recommend you to use the client.
Thank you for your understanding and patience. If you have any questions, please feel free to reply.
Lillian | Microsoft Community Support Specialist