I have another post [1] where I ask why whitelisting a site would cause other traffic to be blocked, but maybe the real question is whether or not this particular feature supports whitelisting IPs.
This is the feature I tried to implement to solve my whitelisting needs:
Content Filter Configuration on RV320 and RV325 VPN Router Series
[1]: https://community.cisco.com/t5/small-business-routers/why-does-content-filter-gt-allowed-domains-on-rv32x-block-sites/m-p/3702360
[2]: https://sbkb.cisco.com/CiscoSB/ukp.aspx?login=1&pid=2&app=search&vw=1&articleid=4231
