Is TWRP OS-version specific? I have a Vsmart Joy 1 phone, running VOS/Android 8.1.0

I found a port of TWRP recovery for Vsmart Joy 1s here (translation), but it says "Android 9.0 VOS..."

Does this mean that I should/have to upgrade to VOS/Android 9.0 to be able to use TWRP properly (the end goal is to root the phone)? Or, can I flash it on my phone as is, without upgrading?
yes, TWRP is built OS-version specific  

the reason is changes in android versions may differ in  


encryption type
file system type
partition layout
mount point


most (if not all) updates are backwards compatible. that means the TWRP is ready for android 9 but you can still run android 8 on your device