I also have tinnitus, and hearing protection that doesn’t attenuate low frequencies gives you an additional kind of tinnitus for low frequencies because it puts them into sharp relief. You then have an internally generated extremely high pitched sound, nothing in the middle, and the only thing that actually makes it to your ear is whatever low frequency sounds are in the vicinity.
You can pair earplugs, bose noise cancelling headphones (inserted in the ear, on top of the earplugs) and earmuffs. It’s an uncomfortable fit, and will sharpen any remaining bass that the noise cancelling doesn’t get to.
For tinnitus, you can pair earplugs, in-ear headphones, and earmuffs (or earmuffs with embedded speakers), and play active white fan noise. This masks your tinnitus, and if you pick a fan recording (download from YouTube) that has some bass in it, it will effectively mask environmental bass. It takes time to get used to.
These are both extreme options, with nothing in the middle. However, for a tinnitus sufferer, active noise is actually good for your tinnitus, because the other sounds have a lateral inhibition effect on the neurons of your tinnitus frequency, which are hyperactive. Unfortunately, listening to white fan noise for too long can become a dissociative. (I have logged thousands of hours), and wearing headphones over earplugs can be uncomfortable. Wearing earplugs too often can also irritate the ear canal, not to mention the risk of putting something in your ear so many times.
If we could do a better job at attenuating bass, it would actually be a big win because bass in your white fan noise is kind of annoying, especially for sleep.
I am currently using this earmuff from 3m which has an NRR of 30. It has multiple layers, hard to say how many. The foam layer is removable, and could tolerate a marine sealant layer (that sealant takes a week to cure!) under the foam.
In terms of low-frequency aircraft earmuffs, I don’t see anything aside from a helmet that might be specialized for low frequency sounds. This could also be the crux of the issue - low frequency sounds arriving through the skull from all directions, instead of just through the ear canal