Besides the sibling comment by Gare to change the default, you can do this on a ...

		no_news_is on Feb 10, 2023 \| parent \| context \| favorite \| on: The Future of Thunderbird Besides the sibling comment by Gare to change the default, you can do this on a per-folder basis by right-clicking, Properties... and checking the box: "When getting new messages for this account, always check this folder"