It doesn’t sound like this applies to you. Yours sounds like it may be wax build up, water/liquid/perspiration got in, or simple age. Except for the liquid issue, you likely will have seen audio degradation happen over time versus abruptly. But as an FYI, you can go to General Settings > Accessibility > AirPods > Audio Accessibility Settings > Headphone Accommodations > Custom (I believe there is a more direct route). I haven’t used this in a while and never on a non AirPods Pro (apologies if this doesn’t apply to AirPods 2). But I recall it has a sound check test which will give some ability to, what I’ll call, check and enhance the volume on AirPods. But also note a user can cause the audio to be notably lesser too (turn off accommodations, see if default sounds better).
If it is age and needs replacement, here is a low cost suggestion: the AirPods Pro 2 intro is likely coming in 2 or so months. These going on sale may see friends or family (or acquaintances of them) getting rid of their existing AirPods on the cheap. Aftermarket on AirPods is an interesting dynamic. Provided you don’t mind buying used and performing a (careful) deep dive cleaning, this may be a great option ((though hopefully you can remedy your existing AirPods 2. BOL))