My information pertains to the US, but this may be the same (or relevant) to Chinese market phones. You likely have the European spec phone with Chinese software.
In the US, the carriers known to lock the bootloader without permitting unlocking are AT&T and Verizon. T-Mobile has left the OEM Unlock option be on a lot of phones (but likely not all; you need to know with them), so some are unlockable. Sprint is a complete unknown to me and does their own thing without a care in the world, so it’s hard to know.
The way LG does it is they have a whitelist on the phones that goes by the model number. Ex: You can’t unlock a LG G4 H815 (AT&T) since AT&T hates power users and loves end users, but the Euro spec H810 can be. While LG isn’t completely restrictive, the device support is limited. While this lets you flash custom ROMs on the phone, the baseband is still locked to changes outside of the carrier subsidy lock. Unless you can find a way to force the matter like we used to do with the HTC phones years ago, the cellular radio isn’t open for modification.
If you’re okay with the obvious risks, the instructions on how to unlock the bootloader can be found here (LG Developer).
While I’m aware of how to deal with the bootlader, I’m not sure about altering the basebands on the phone. LG locks this down pretty good (unlike the old school HTC phones, which were more or less left locked by HTC but were a joke in regards to forcing it to happen), so you need a *really* good radio exploit that’s permanently unpatchable - even with hardware revisions. Most people have no need to do it, so there’s not much to go around like the HTC radios of the past.
Motorola is the new old school HTC we know from years past before they worried about the mainstream market and left power users behind. Sure Motorola locks the cellular radio down (those days died with HTC sadly) like LG, but they make it stupidly easy to unlock the open market phone bootloaders (outside of the Prime phones by demands from Amazon). Honestly, the ability to weak the radio settings doesn’t matter anymore since most new phones have full support (factory unlocked) or nearly 100% of the bands of the unlocked phone (carrier locked). The carriers may disable a few they don’t want to certify, but that generally stops at something like AT&T blocking the CDMA radio (they’ve been GSM from day one) but they don’t mess with the GSM bands the phone supports much or at all.
Verizon used to be dicey, but since they started selling full GSM phones with CDMA backup radios it’s been less of an issue - but you need to be careful. Sprint plays with the radio more then they probably should on most of their branded phones.