[Magisk] intel_core_i7:
Locking a global device with a global rom from different regions is safe, there are services to flash the current global's "global" rom (MIXM at the end of build number) to Indian/Taiwan/Indonesian variant rom (IN/TW/IDXM at the build number) via EDL, and you guys might have known that you can only boot from official software if flashed with EDL (EDL requires authorized token from Xiaomi service centers, so those accounts are sold somewhere, for a fee of course). I haven't actually seen someone locking his global variant device on Chinese ROM, so yet to be verified, but some claimed it works.

Devices from different regions (like above) and China both have hardware and software difference:

With software:

Chinese version are more tailored, stable (better system responsiveness, more features, etc.) but the lack of full Google services means by default apps not from China will be axed by the system where any background tasks will be terminated right at the time you close the app, meaning delayed notifications for several hours, missing calls if it's an instant messaging app. It can be overcome by disabling battery optimization for those app, but hiccups can happen. The lack of full GMS also means no android auto, no google assistant, bad GPS reception, and many other GMS related stuff are cut off, it's even more stripped down than those Gapps pico packages you can flash on your custom ROM. TLDR: Stripped down GMS and tailored to Chinese users with their own mainland services. Chinese ROMs also has most system languages stripped out

Global version has full GMS with all of the Gapps Google deemed "system" app like Youtube preinstalled but the stability, responsiveness and features from Chinese ROM has been massacred as a result.

Different global variants can also have difference, mainly whether Xiaomi or Google dialer is used. Mi dialer has automatic call recording without an announcement robot voice, but lack the automatic spam call blocking from community reports of Google dialer.

With hardware:

Most common one is NFC. Countries with low NFC usage for payments/transportation or where they need to cut cost will have the chip not installed

Camera sensors, some examples

Redmi K40s/POCO F4 (my previous phone): same codename, with 48mp Sony IMX/64mp ovb sensors, respectively; Redmi K50 ultra/Xiaomi 12T Pro; and more

Charging speed

Different cellular modem or eSIM support. The POCO F5/Redmi note 12 turbo has different modem between China and global variants, so China users on Global ROMS or custom ROMS where the maintainer doesn't acknowledge the difference will suffer from cell signal loss; Xiaomi 13/13 pro Chinese region doesn't have eSIM while global does, flashing global variant on Chinese will not make it work because it lacked the hardware itself

Software/hardware differences are results of different regulations, cost cutting or to deter people buying from cheaper regions and then flashing roms for the region they're buying. While the variants share the same name and ROMs from different regions can be cross-flashed, hardware differences may exist and ROMs from different regions will not work properly (some can be patched if have different hardware but some outright cannot because it lacked the hardware required from other regions)

People only flash roms from other regions when the two devices share 90 - 100% of the hardware configuration (lack of esim and nfc can be ignored because there's usually no need for it) to have full GMS, user's native language and the mi dialer for call recording.

I don't really know why you guys are surprised or confused about this since pretty much every manufacturer do this, examples:

LG with different software for 5G/VoLTE between regions, and one camera being axed on the G8 outside of Korea

Samsung with Exynos/Snapdragon shenanigans, and the CSC thing.

Pixel with International/Japan variants (Global has NFC-F disabled by software and Japan with NFC-F has the exclusive Google wallet UI to support their own osaifu-keitai)