There are actually apps which will "appify" webpages/websites for Android, or were the last time I needed one. They've been aroubd a long time. I assume they still exist.
The functionality is literally built into both Android and iOS. For example, I've got some of my self-hosted services linked on my home screen. On Firefox for Android you just browse to the site, click the 3 dots, and then under more its "Add to Home screen", Chrome works similarly.