I have not tested PHP 7.1 on WP 5.7 yet, I stopped when I got a working combination. I’m one of those rookies who doesn’t have a testing environment and puts everything on just a production server, once we get our stuff sorted, I’ll test PHP 7.4 with WP 5.5.3 then if it works, I’ll step up to WP 5.6.2. Since we’ve had no trouble with image uploads until the newest WP update, I now assume it wasn’t PHP, but I’ve already demonstrated I’m no authority, that’s pure conjecture.