Firewall on Android smartphone

Hello, I read online that to protect oneself on public Wi-Fi, one should use a VPN. My question is, if we only use a non-root firewall without a VPN application (since the smartphone's system is not rooted and this firewall uses the smartphone's VPN connection) to allow only the apps we want to connect to the internet, is it not enough to protect against attacks via public Wi-Fi?
The problem is that we cannot use a non-root firewall along with a VPN, is there not a solution to protect oneself on public Wi-Fi without using a VPN application? This is important, thank you for your answer.
Best regards.