The error in your screenshot explains the reason why right, unpin a field first and then you can add the field as pinned.
Pinned fields are personal, but the issue there is whit this there is no exact limit on the number of fields, but it's limited on the number of characters, see JRACLOUD-78946
Even if I remove the some of my pinned values I still get error
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See the Jira issue that is linked in my previous reply.
This is what your are running into.
What if you remove all your pinned fields and then try or is this field from a 3rd party app as these fields can't be pinned.
Does it work in another browser or incognito window?
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