I just checked on Linux (Thunderbird 128.5.2esr, Opensuse Tumbleweed) and the behaviour is the same.
If I search “PMASUP236”, it returns the email as a result.
If I search “SUP236” it does not.
This is using the normal search function (top of screen in current version). Quick Filter does not look at attachments at all by the looks. The “Attachments” toggle is only a has / does not have attachment filter.
Nothing, cause I’d rather choose what to ignore on the fly rather than creating the same bubble I get stuck in on every other social media platform.