I bought watch ultra from Lebanon and for some reason I cannot use the SIM card of my provider in Cyprus. can someone help?

A Watch bought in Lebanon could be from any source and intended for ant country! To see which network providers in your country or region offer cellular service for Apple Watch according to model number, refer to the chart below. 

Apple Watch - Carriers - Apple

Only Cyta provide the right eSIM for your iphone and Watch (needs to be on both) and Watch needs to be model A2684

Worst thing is you have No Apple Support and No Warranty for Watches bought outside your home country

You can enjoy the Ultra as a GPS-only watch with almost all the regular features, you just need to keep your iPhone with you. That is something that most people do anyway! Turn off the cellular in the Watch.