K8y hence need to take out battery, if kill switches don't stop the accelerators.
I think it is possible that a misunderstanding may be in operation.
I am unaware of credible reports of mass audio snooping. Things like Pegasus are inherently narrowly targeted snooping (because if there are too many targets than the vulnerability gets discovered and patched).
If you, personally, have reason to believe that you, personally, are likely to be targeted by somebody with access to tools of that expense and focus, I would recommend that you hire a security consultant (CISSP, CISA, or equivalent) and an attorney. This is because random advice from people in online forums is not a reliable replacement for a serious security professional evaluating your situation. It is also because even the most secure phone imaginable will not protect against serious targeted surveillance, which may include many non-phone tools.
Hopefully over time we can get off-the-shelf phones that have better hardware security than the phones we can get now. That would be great. But somebody who genuinely needs a seriously-hardened phone now, genuinely needs a phone with a removable battery now, etc., has many other security needs and should talk to a professional.