It's a valiant effort, but I think it's pretty clear who it is: Bob Reynolds a.k.a. Sentry (played by Lewis Pullman). Those who have been paying attention to Thunderbolts* will recall that Bob was prominently featured as a character in the first trailer for the blockbuster that arrived in September,

The final Marvel Phase 5 movie's second trailer reveals that Bob Reynolds, the MCU character who'll be played by Lewis Pullman, is actually a superpowered being. Not only that, but he's also harboring more than one secret within himself – and one of them is of the potentially world-ending variety.