My apps are stuck on iPhone 12 after transferring data from another iPho

Some things you can try. Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

Have just upgraded from iPhone XR to iPhone 12 Pro.

Data transferred from old phone, no problem but Apps stuck on loading. Have already switched phone off and on again. That succeeded in Apps moving from waiting to loading but nothing els. Incredibly frustrating; nothing ever as simple as it should be when upgrading Apple phones!!!