Everyone has this issue with texporter. You are not doing anything wrong its just the way texporter renders out the information. To fix this issue just select the area around the head so its right up against the seems. Then expand the selection 2 to 3 pixels out. Once that is complete just fill it in with the base color.…
I solved my problem. I exported unreal engine 5 manny skeleton. I created a biped. I've done a link constraint unreal skeleton with biped. Biped ready for animation :)