There are plenty of free email services around, but they often require you to give up a measure of privacy and control. Some, like Google, have historically served up targeted ads based on the contents of your email (though the company has said it no longer does this). Others, like Apple, want to lock you into their ecosystems so you never buy a device or subscribe to a service offered by another company ever again.
It’s a refreshing change to use a “neutral” service like ProtonMail (bonus: the company is actually based in Switzerland). You’re not being pushed to use a particular browser or smart assistant or chat service while you’re checking your messages. ProtonMail is an option if you think the tech giants have already claimed enough of your digital life.