Apparently, there’s a typo in the WP Increase Upload Filesize | Increase Maximum Execution Time plugin (not really necessary, but convenient) which prevents its settings page from working:
In wp-maximum-upload-file-size/includes/class-wmufs-helper.php, line 32, update
function convertToBytes( string $from ): ?int {
to
function convertToBytes( string $from ): int {