If you don't watch Falcon & The Winter Soldier then Sam goes from accepting the role of Captain America in Endgame from Steve, to being Captain America in Brave New World. There is a moment in Endgame where Sam isn't sure he's earned it, but that's part of the conversation with Steve.
If however you do watch Falcon & The Winter Soldier you discover that Sam did wrestle with the idea of being Captain America for more than just a moment. During the series Sam grows as a character and ultimately does accept the role of Captain America.
For the purposes of the Captain America character The Falcon & The Winter Soldier is not required. It's a nice bonus to his character and I would recommend it. It's like watching The Avengers having not seen Captain America 1. You can enjoy the Captain America character without having seen his origin story.