Baldur's Gate 3 is absolutely massive and is a game that you likely won't be done with for a pretty long time, but once you're done you might want to go back to the game to make decisions that you didn't make in your first playthrough and when you do, you might want to change things up a little bit. Luckily there are already a few pretty great mods for Baldur's Gate 3 that you can use.
Tav's Hair Salon
Tav's Hair Salon does what it does on the tin really, it adds a whole host of new hairstyles to the game, all for the player character. They're all additions to the regular hairstyles too, so you'll just have a whole host of choices. Now we just need a way to change our hairstyle in the game itself.
Customizer's Compendium is another mod that adds a lot to the initial customization option, but one of the coolest things that it adds is a lot of new color options for the game. It basically adds hairstyles, colors, horns, ears, and other options that were previously only available as part of NPC models, meaning that you can finally look like your favorite background character.
5E Spells adds a WHOLE bunch of spells from Dungeons & Dragons Fifth Edition which aren't available in the base game but are available in the standard game of D&D, meaning that you can finally create the Dungeons & Dragons character of your dreams. This mod still leaves out certain spells that are incredibly overpowered such as Wish though, so don't expect to walk your way through the entire game.
Improved UI does exactly what it says on the tin. It subtly changes up the UI so that everything looks just a little bit cleaner and specifically works the best when it comes to players on PC who are playing with a mouse and keyboard, as it'll make everything just feel a lot smoother.