I doubt this will work - people have tried this in the past to circumvent the EU-volume limit, but iPhones differentiate between the (changeable) region setting and the region of sales, i.e. the region the iPhone was made for, basically different hardware with different model number. So going into an EU-iPhone settings and changing the region to Australia will not change it being an EU-iPhone and thus not remove the EU-volume limit. Probably the same here - but might still be worth a try.
Here someone posted a screenshot from their chat with Apple support. According to this it is a permanently-on feature as of 14.2 in Canada, EU, Israel, South Africa, Turkey, Ukraine, UAE, UK, USA. Those who do not have it yet will get it as soon as they reinstall.
I'm looking into jailbreaking now. That in itself was easy enough, since I use an old SE, but where to find this setting...