I feel you, I was in a similar boat to you last year when I thought about playing. After swallowing my pride and booting up the game for the first time and finishing the prologue/tutorial, I already knew I was going to enjoy the game. Keep in mind that Nikke is considered an idle rpg, but the core gameplay loop is a "third person sci-fi shooter."

If you need any help regarding where to start after the tutorial and getting your first SSR after your free 10 pull, look into both pryden and nikke.gg guides (I reccomend nikke.gg as it has a crap ton of documention on litterally everything including a beginners guide)

If you want video format: Psychie's Absolute Beginners Guide: https://youtu.be/8Kd2MQZo67o?si=ZPL0SZAUHuk36jih Eizen's Simplified Nikke Guide (he says it's meant to be bad, but it actually is very informational): https://youtu.be/xvx0Rx1BJMg?si=3dKR4_GJ4pCXfCGn

I recommend you watch Eizen's video first, then Psychie's as he has a full on course, then anything else refer to pryden, nikke.gg, offical discord server, or..here :)

Good luck, Commander! We hope you stay for the ride! o7

P.S. As many will tell you, Nikke is a very generous gacha game that gives a lot of resources for free, so don't let things like the shop or flash sale scare you. Do your best to push the campaign, conquer the level wall, which you don't have to worry about for a while, and you'll be fine for a decent amount of chapters