MS List Column Width Forced

You are seeing every column expand to full text width, including multiline fields, although those views previously allowed narrower manually sized columns. Because this began across several lists at once, it looks more like a modern Lists view regression than a data change. Exit grid view and try dragging the right edge of a column header, then save the current view. Repeat in an InPrivate window and a new view with no JSON column or view formatting. If resizing works there, reapply formatting one column at a time to find the conflict. If every list and browser is affected, check Microsoft 365 service health and open a support request with the tenant, list and view URLs, timestamps, and screenshots. Avoid changing column types, because that will not correct a rendering problem.