You can't tether for free on Wi-Fi unless you have a tethering plan, but you can tether using Bluetooth or iPhone USB.
On an iPad, after bringing both devices into pairing mode, with Personal Hotspot on, select the iPhone to begin pairing. Verify that the code on-screen matches the iPhone. If they match, tap pair on each device. This will establish an Ethernet-based Bluetooth PAN whenever you connect. When done, go to Bluetooth in settings, tap the (i) next to the iPhone, and tap Disconnect. This will restore Wi-Fi on your iPhone, which was turned off for tethering. To connect again, select the iPhone on your iPad's screen while Personal Hotspot is turned on.
For a Mac, it's a bit different. You can't use a Bluetooth PAN because the feature was removed in Monterey v12.0.1 To remedy this, you need a connector cable. USB-C to Lightning (if iPhone 14 or older), or USB-C to USB-C (if iPhone 15 or newer). Connect the device, and wait for it to populate in the Network tab in System Settings. Click the (…) at the bottom, and click "Set Service Order". To make the services work correctly, you need to set the order to "iPhone USB" first, then "Thunderbolt Bridge", and finally "Wi-Fi". This is because of a bug that prevents tethering from working unless at the top of the list. Thunderbolt Bridge is there to prioritize Ethernet if a Thunderbolt Dock is connected. And if all else fails, Wi-Fi is a last resort. Once you set this order, your Personal Hotspot will kick in until you disconnect the iPhone, and all you have to do is visit a website like this one to test it out.
And the best part is: If you don't have a tethering plan, most carriers will allow these types of tethering at no additional cost.
Hope this works for you!