The "boomer" in "boomer shooter" refers to the style, not the release date lol. Most games with that tag are actually pretty new. They're just shooters that are mechanically similar to old shooters like Quake and Doom, so you're typically gonna have a mix of these traits:

• A wide range of weapons with unique uses (think rockets, railguns, shotguns, machine guns...)
• Chapters that you can complete in any order but the levels in them are completed linearly
• Colored keys to open colored doors
• A level-end screen when you reach the end of a level that tells you your completion time and what % of items/enemies are left
• And my favorite part, a lot of them have advanced movement techniques, which are usually identical to Quake (if not Quake 2/3) like bunnyhopping and rocket-jumping

I recommend Dusk or Ultrakill if you wanna try a really good (and cheap) boomer shooter that came out in the last few years.