Thanks! That worked for me for thread links, but for some reason my forum home page doesn't have any Twitter card at all.
By default, Twitter uses the Metadata logo URL at admin.php?styles/default.1/style-properties/group&group=basic#sp-publicMetadataLogoUrl for threads, which for me is a wide one that gets the sides cut off on Twitter. So I set mine to the Icon URL (512x512). Unfortunately that had no impact on Twitter not displaying a card for my forum home page.