Looking for a good shooter game?

NO Fortnite

however, it can still be Battle Royale.

Free would also be cool but doesn't have to be.

Best with military vehicles such as tanks / helicopters etc.

CoD Warzone, Apex, Hyperscape, PubG, all weapon games with Battle Royale

Warzone maybe?

Rising Storm 2: Vietnam

post Scriptum

Hell let loose

Red Orchestra 2

Here are the free ones:

Call of Duty: Warzone
War Thunder
Heroes & Generals
Planetside 2
Counter Strike: Global Offensive
Valorant
Apex Legends
Paladins

Here are the chargeable ones:

Call of Duty: Modern Warfare
Hell let loose
post Scriptum
Squad
Battlefield 5
Battlefield 4
PUBG
Rainbow Six Siege
Insurgency sandstorm

Call of duty modern warfare (chargeable) or, as an alternative, Call of duty warzone (free). Great graphics and great gameplay!