What about the sound effects?

But neither of those are what happened.

 

There’s likely a huge database of sound effects and they just mix it in partly out of it being established and partly pure nostalgia. It may even mostly be due to whoever is doing the sound mix liked that particular sound and didn’t care which era it came from.

 

None of the sounds in Disco bother me. The only time a Trek noise has, was a slowed-down TOS communicator sound being constantly played on the NX-01 bridge.

I love the TOS/Kelvin noises, since they're unique to Trek. You hear them and know it's Star Trek. The TNG-style computer sounds are far more generic to my ear.

 

It's not just the wrong era, it's also the wrong galactic power (Klingon and Romulan alert sounds on starfleet ships)