Hi @Rebecca Mack ,
What's the version of your Outlook for Mac(Outlook>About Outlook), please ensure that you have updated to the latest version of Outlook.
Now a large number are not showing
Considering the issue occurred only recently, have you performed any special operations before it? And could it display normally if you create a new task via flagging emails?
Did these missing tasks have any similarities(Due Date or others)? Could you find them via Search field in Outlook?
If you could find those tasks via Search in Outlook, the issue may be related to your View settings, it's suggested to check and change your setting to test.
Also, I have tested on my Outlook for Mac(version 16.44), but found all tasks in my Exchange account display normally, so it seems to I haven't reproduced your issue. Considering you could find those tasks in your web mail, the issue may be more related to your client. Based on my research, I found a similar thread, which mentioned the OutlookSearchRepair Tool may help us resolve the disappearing tasks, it's suggested to download and use it by the article mentioned to check if it could also be helpful to you.
Update:
For the task in New Outlook for Mac, please kindly understand that Microsoft teams are indeed working on adding support for task feature in the future, you could vote this idea in uservoice, which may increase the priority for our engineers to create a possible option or feature that can be included in the future updates of the program.
By the way, for your current normal use in client, you could also try to turn off "New Outlook" and switch back via click this button. We understand this is inconvenient, but we are working hard to bring back support for this feature as soon as we can.
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