iPhone X stuck in reboot..

Restart your iPhone X or later. Press and hold the Side button and either volume button until the power off slider appears. Drag the slider to turn your device completely off. After your device turns off, press and hold the Side button again until you see the Apple logo.

Restart your iPhone, iPad, or iPod touch - Apple Support

https://support.apple.com/en-in/HT201559

See if the tips in the following article help resolve the issue.

How to fix an iPhone X that is stuck on Apple logo, infinite boot loops [Troubleshooting Guide] - iKream