The Priorities tab is a legacy feature and will no longer be automatically added in your 1-on-1's in Fellow. It'll only be there for people who have had it before it's been fully removed from the product and can still be found in the 1-on-1 section with your direct report/manager (1-on-1s where you have a reporting relationship).

When you go to the Home Panel section and click on the name of manager/direct report.
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Under the 1-on-1 header, you will see a few tabs across the top and you can find your Priorities tab there.