Exporting transparent video in Premier Pro 23

Hi i trying to get my alert boxes in twitch made. i use after effects to make the quicktime file with alpha and the trancparent backround.. i after use premier pro 23 to export it to webm, i dont get the 8bit + alpha, and not the use only alpha.. so i can remove the backround.. when i export it i have a big black squere around my alert..