I own MSFS2024. You can not buy it on CD, it is only available via Steam. In fact it is impossible to use MSFS2020 or MSFS2024 without your computer being online because it streams all the imagery and data from Microsoft's servers. There is simply too much data, it can not be all stored on a CD or DVD or even blu-ray.
It is quite simple to purchase and install using Steam, but if you have issues with not having a "hard copy" of the game, you're gonna be outta luck, it just doesn't exist. BTW, you will need a fairly beefy computer to run it. I use a Intel 13900k + RTX4090 + VR headset. I don't play it often actually, but perhaps once I learn how to land without crashing I'll play it more often.