Loading stopping at 75 percent at the launch of the Clash Royale is a known bug waiting to get fixed by Supercell.

Airplane Mode

1. Close the game and enable Airplane Mode.

2. Open Clash Royale again and turn off Airplane Mode when the game asks you to reload.

Restart Wi-Fi

Turn off Wi-Fi and then turn it back on after 30 seconds.

Updates

Check your app store for any new updates.

1/1/2025

Sueprcell's answer to reports about this problem was "we are aware of the problem and trying to fix it.", so if nothing worked the only option would be to wait for a fix update.