Mac Pro (6.1) Blacking out

My 27" Thunderbolt Display attached to a 2013 Mac Pro running Mac OS 12.7.6 has started randomly blacking out while using. Sometimes the screen comes back after a couple of seconds sometimes not and it will restart. This morning I removed the cover and removed dust etc.For most of the day seemed fine with normal Operation but now have gotten a number of black outs.

Any thoughts welcome TIA.