Linux is pretty much universally free, with the exception of a few select distributions like Red Hat Enterprise Linux (and even then, there's variants of RHEL that are free like CentOS and Fedora, the main attraction for RHEL is paid support).

Most distributions are fairly similar, these days, with the main differences being the desktop environment (i.e. how the UI looks and feels), the update cadence (some distros are much more aggressive about deploying updates to the software and utilities underlying the distro, which gives new features faster at the cost of breaking things more often, while other distros prefer to stay on older, known-stable versions longer, at the cost of being slower to deploy new features that sometimes a program needs to run), and the methods used to configure settings (some distros go out of their way to make as much configureable in the GUI as possible, while others are primarily configured through console commands, and others like Gentoo expect you to manually compile pretty much all the software yourself–this makes it extremely customizable, but extremely difficult), and the default file format for package installation (rpm, deb, flatpaks, snaps, etc).

My personal recommendation is to check out a few of these:

• Ubuntu

• Linux Mint (or Cinnamon)

• EndeavorOS

• Pop!OS

I also recommend that when you first format the disk, you make two partitions: one smaller 50-100 GB partition for the root partition (where Linux stores its system files and software), and a larger partition for /home, which is where all your personal files are stored. This way, you can easily swap between different distros without needing to really worry about losing your files.