Does it make sense to use a VPN on an iPhone when Apple and its iOS have fewer security issues than other platforms?

Even though iOS has a reputation for strong security, no platform is entirely immune. VPN provides an additional level of security, protecting your data from eavesdropping and allowing you access to content that may be blocked in some regions for whatever reasons. So yes, it definitely makes sense not only for privacy protection.

Are there free VPNs that I can use on iPhone?

Yes, there are free VPN services , but one needs to be careful. Many free VPN services might sell your data to third parties or do not provide adequate security. Always thoroughly check the ratings and reviews of the service before using it. Especially choose from well-known brands.