As per interoperability matrix, you cannot manage ESXi 8.x on lower vCenter version i.e 7.x
https://interopmatrix.vmware.com/Interoperability?col=1363,&row=2,
You can try it in lab and see, in the past when I tried to add higher version of ESXi in a lower version VC, it didnt allow me to add the node. However, I haven't tried on versions 7.x and 8.x