If I recall correctly the maximum Noise Reduction Rating (NRR) for earplugs and earmuffs is around 30db. You can combine the two for a slight increase in hearing protection but you still hit a limit because of bone vibration.
Is there PPE out there to go even further beyond this? Where would it be commonly used?
You understand that all of those devices have passive noise isolation, right?
What the electronics are doing is actually playing back noises that don’t cross certain thresholds. (Like people talking.) so you can “hear” them, but really it’s the speaker drivers you hear. The best will also filter out background noise, but the protection comes from the passive protection.
(Which is again different from acoustic filters, which basically create a chamber that alters the noise wave forms to passively attenuate things that are too loud.)