VMOS Pro is an Android virtual machine (VM) app. The availability of specific ROMs (especially older 32-bit root versions) changes frequently as the app updates. Version 7.1 is a relatively recent release, and most official ROMs for it are 64-bit. You may need to source a custom or archived 32-bit ROM.
You can run both VMOS Pro 7.1 (for 64-bit apps) and an older VMOS (for 32-bit root) side-by-side. Vmos Pro 7.1 Root Rom Download 32 Bit