You should be able to do this from a pubsec tenant. Insure that you are logged in to the correct tenant on the actions/triggers that call the SharePoint site by clicking the ellipsis on the step and verifying the pubsec tenant account under My connections (green box):

Also, make sure you are utilizing the correct pubsec Flow environment, by clicking your name in the top-right of the Flow page, and verifying the checkmark is next to the the correct Environment: 
If that doesn't work, you may try re-adding your credentials in the Flow connector for SharePoint in the Data > Connections page:
You can Delete and re-add, or you can select Switch account: 

NOTE: Deleting and/or switching your accounts for the connector will not break existing Flows using that connector.
If this reply has answered your question or solved your issue, please mark this question as answered. Answered questions helps users in the future who may have the same issue or question quickly find a resolution via search. If you liked my response, please consider giving it a thumbs up. THANKS!