Okay so I’ve seen all the debaty posts about this and why Steve wasn’t able to lift Mjolnir at the party in AoU.

Some say that Steve could lift it all the time, others say he couldn’t because he didn’t tell Tony about the death of his parents. I’m going to jump over all that CW ugliness now and not debate any of that.

What I am going to tell you all is this - Steve Rogers is known to be a master tactician. Which is officially defined as: a person who uses a carefully planned strategy to achieve a specific end.

Now let’s fast forward to Endgame. When Steve lifts Mjolnir it is at a critical point in the battle between Thor and Thanos. Thanos is literally pushing stormbreaker into Thor’s chest. He’s going to kill Thor. Steve has to strike and he has to do it fast and with prejudice. He cannot take a chance. Would someone that is a master tactician go for a weapon he knows he cannot lift, cannot use? Would he? No. Steve lifted Mjolnir and used it at that moment because he knew he could. There’s no other explanation. He wouldn’t risk a maybe. Thor is moments away from an ax blade in the chest. Steve picked up Mjolnir and beat the crap out of Thanos.

Therefore Steve could always pick up Mjolnir. Steve is worthy. Always.