@Bri If it's an app you have on your account already, you can still find the last version of iTunes which supported this, 12.6.something but I'm not sure how well that works for installing on newer phones. iMazing also lets you do this, though here if you want to avoid headaches the mac version was way easier to use last time I used it. The Windows iMazing is one of those winforms apps where most things that read as a bunch of class names and you need a lot of object nav to find anything. If it's an ipa you that wasn't on your account, you can use sideloadly on either Mac or Windows which will install and sign it with your apple account.