Usually that's not a reliable way to identify a unique user. Given the prevalence of NAT, re-using IPs by ISPs with DHCP, and a host of other reasons. (That's not to say there aren't ways to fingerprint users across devices and browsers.)
A service ISPs should offer as standard is regularly randomising your outbound IP from their pool for all but a whitelist you specify. So you can have a static IP for say you work firewall, but are harder to track otherwise
