Hello,
In the V200R010C00, only the S5720EI, S5720HI, S6720S-EI, and S6720EI support the set vrrp max-group-number command.
To change the maximum number of VRRP groups, you can only upgrade the device to V200R019C00 or later version, so the number of the maximum number of VRRP groups on the S5720SI can be set to 256.