While Android is based on a Linux kernel, it has been heavily modified. So, that does not make it a full-fledged Linux-based operating system. Google is trying to get the Android kernel close to the mainline Linux kernel, but that is still a distant dream.
For normal users though, they will consider whether their banking app runs on the phone, their favourite game, insurance company app, etc. So possibly an Android emulator of sorts could bridge the gap, but there are a small percentage of apps that are very locked down to official app store versions with no rooting etc.
An advantage though of a pure Linux phone, is that anything developed or workable on normal Linux as an OS, should run perfectly well on these phones, as will anything that is browser based. Linux now has Snap and Flatpak packages that are build once, run across all distros, so the landscape has been becoming more standardised.
So, if you are an enthusiast or want to support the development of such phones, you can consider getting one of the devices.
See Linux Phones: What are Your Options?
Not Android, not iOS? Looking for a real Linux-based phone? Here are your options when it comes to a Linux-based smartphone.