You can sideload as many apps as you want with AltStore, but due to Apple's restrictions only 3 sideloaded apps can be active at a time. If you try to activate more than 3 apps, you will be prompted to "deactivate" a sideloaded app first. Deactivating an app will make AltStore back up all its data before removing it from your iPhone or iPad, freeing up a slot for you to then sideload another app. Alternatively, you can manually deactivate an app at any time by long-pressing it in the My Apps tab and pressing "Deactivate".
Deactivated apps will appear in a separate "Inactive" section on the My Apps tab. Once deactivated, an app can later be "activated" by pressing
ACTIVATE, which will cause AltStore to re-install the app and restore all its data.