Yes, ISP proxies support IP whitelisting. To use this feature:
Find ISP proxies in your dashboard.
Scroll down to the Whitelisted IPs section and click Add IP (1).
Enter the IP address (2) you want to whitelist and hit Save (3). Also, if you add notes to your IPs, it will be easier to manage them later.
Note: Each IP address can only be whitelisted by one IPRoyal account at a time.