Keep in mind that we are not spoon-fed everything. The Avengers obviously spent some time together that we haven't been shown. The fact that Wanda went from new recruit in Age of Ultron to part of the team at Lagos in Civil War is proof of that. We don't need to see stuff like that because it's obvious they spent time together training and building the team.
In the same vein Wanda, Strange and Wong all fought Thanos and his army together in Endgame. They were also all present at Tony's funeral. Unless we assume everyone showed up and immediately left again it's safe to assume people actually talked with each other.
I mean you aren't questioning either that when Wanda walked into the SWORD HQ people knew who she was, right? She was an Avenger so obviously people know her.
I get where you coming from but this is a clear case where the storytelling medium has its limits. Imagine if you would actually have to have every single character in the MCU making acquaintance with each other first. That runtime is better spent on devoloping relationships that matter.
It's obvious Strange and Wong weren't friends with Wanda but as stated it's not a stretch to assume they at least knew each other considering their status in the world.