Hi, how exciting! Kudos to you for taking up PC building.
Let me start by saying that this is an excellent build for a first. Not only will it not be difficult for you to build it, but it also packs quite a punch. There are also no compatibility issues as far as I can tell.
It is a little underwhelming for 1440p120hz on AAA titles (games like CoD, Battlefield, Tomb Raider, Red Dead Redemption II, and so forth), which may require you to reduce the settings a little bit to achieve your target. Though you should be able to achieve that in many games.
This is a build I would be comfortable recommending at any time, but here are a few points that you might want to consider:
1. If you're planning on trying your hand at overclocking someday. I would recommend opting for the B450 Tomahawk MAX, it's a pretty popular and well-known board for its good and stable overclocking experience. Although, the one you've picked will allow you to overclock as well.
2. Please ensure that whichever RAM configuration you've selected is a dual-channel kit. Meaning that the packaging contains 2-DIMMs (or two RAM sticks). It is advised not to purchase two separate sticks. As for speed, the 3600MHz you've picked is a well-recommended speed.
3. A 1TB NVMe storage can come in quite pricey. Since this is primarily a gaming computer, you'll find that 1TB won't get you very far (especially with games like CoD being over 200GB). When it comes to games, there is virtually no difference in speed between installing them on a regular SATA SSD or an NVMe. For that reason, you may want to consider dropping to a 500GB NVMe SSD instead and to add a 1TB SSD for your games for roughly the same price. Personally I install the game clients on my NVMe for snappy experience and install the actual games on a separate hard drive.
4. 750 watts is slightly overkill. You could go for a 650w unit of the same model if you'd like.
5. Don't forget to add more 120/140mm fans as the case only comes with 3 pre-installed units.
--> Please keep in mind that these are just suggestions and things that you might want to consider. You won't go wrong with the build you've proposed.
Good luck with your first build!