Story wise it's self contained. You might be on slightly better footing with the building mechanics if you've played another, but it's different enough that it's not required.

This is my first one as well, I don’t feel like I’m missing anything

Nothing story related to the other ones has hampered me. Missions are all replayable, with full cutscenes where they are. If you want an excellent mech customization + arena + objectives in bite-size chunks with really great boss fights, you won't regret it. It works fully on the Steam Deck too, which is great for quick breaks from work.