Updated to 1909 April update KB4549951 last night. Today the MS Windows Mail app ("Mail and Calendar" app) wouldn't download any Gmail.com email messages, only Microsoft email messages (Outlook.com account). I removed the Gmail account from the app then went to add it back on again, as this has fixed issues in the past.. now the app crashes every time I try to even go to "manage accounts" where you can add email accounts. Nice one MS. Going to try uninstalling.
edit: uninstall / restart / reinstall and set up - seems to be working now. Assuming the Windows update borked it since I hadn't installed anything else.