Lemme reply directly to u so that u are not confused.
Global rom is pretty much like standard stock Android. It's basic and has very few Lenovo touches.
Cn rom, also referred to as zui, is like a manufactured skinned UI, pretty much like Samsung's one UI or xiaomi's miui. It has more functionalities added by manufacturers compared to standard stock Android. (Though with more functionalities also comes with more bugs and glitches)
Both have full google services and every google app like play store, Gmail, etc can be installed. U have to install the google stuff manually in zui.
When u do buy a pad 2020 or pad pro 2020, first thing u need to check is what rom had the seller installed for u.
Go to 'about phone' or 'about tablet' and note the rom identifier as well as the Android version.
1) If it's zui, that means it's on a china rom. If it's Android 10, that means this tablet is possible to convert to global rom using Lenovo's official tool. If it's Android 11, then better stick to zui.
2) if it's a global rom, then u have to check if it's a official or fake rom. Compared the rom identifier and check against the lolinet repository to see if it can be found.
Pad 2020:
https://mirrors.lolinet.com/firmware/lenovo/Tab_P11/TB-J606F/
Pad pro 2020:
https://mirrors.lolinet.com/firmware/lenovo/Tab_P11_Pro/TB-J706F/
If it's found, then it's an official global rom. If not, then it's a fake rom.
For fake rom, just repair it using the official Lenovo tool to change it to official global rom.
https://support.lenovo.com/sg/en/downloads/ds101291-rescue-and-smart-assistant-lmsa
Sidenote: for 2021 models like pad plus and pad pro 2021, they don't need to check. Anything that is not zui are 100% fake roms.