As someone who just got into tennis these are my fav moments to witness (a non comprehensive list):
When they take out the Little Smallest Mixed Nuts Tupperwares (looks like they're in kindergarten having a snack)
Coaches gripping their racquets on the grandstands
When they take out a fistful of four to five racquets from the bag (how many do you have???? How big is the bag???????)
When they take off the clear casing on the grip (very satisfying sound mm)
Shelton and Alcaraz serves (first is power, the second's poetry)
When someone gets hurt and the other jumps over the net to check on them
When f1 drivers attend the match
Casper Ruud's calming aura
When they catch the ball mid air with the racquet
Seeing them smile at each other after a hard-fought point (like, "look at the magic we made together")
Learning how each player builds up the serve
How the crowd starts quiet and gets rowdier as the match gets more tense
Djokovic-Sabalenka friendship
The ATPTour audition videos??? Fire (honorable mention for Texan accent Tsitsipas)
Learning about the big four. Looking back on their matches with awe (honorable mention for the nostalgia factor of the video/photo quality)
Berrettini smiling at the ball boys/girls
The hand gesture they all do for the towels (looks like John Cena saying "you don't see meeee")
Seeing clay marks and stains on their kits
Feeling the energy shift with every point, it ebbs and flows like water
Cheeky swearing in their own language (especially in Italian as I can understand it hehe)
Learning how they say "point, set, game" in different languages depending on where the tournament is held