A distro relying on an out of tree filesystem as default sounds like a really bad idea to me. I didn't know Ubuntu shipped with ZFS in the default kernel.
Also luks and btrfs are good enough, and in-tree. They might not be as fancy as ZFS, but it's a better choice to use as default as they're standard and widespread.
That and their (understandable, but annoying) reluctance to enable Wayland.
They could at least make it optional, but given that they sell computers, I understand why they wouldn't want to enable a feature which may still cause problems...
This is another good example for what I described in my other comment - they only care for their very special setup but break the underlying distro in many ways.
PopOS devs take the work of Ubuntu, add their 0.1% but break a lot of things that work good in [X|K]Ubuntu - that is not helpful for the OS ecosystem. They distribute a broken distro that only works within a very narrow default configuration. Not OK.
It is bad because of the reasons I explained in my other comment.
They pretend to release a whole distro while in fact they are only caring for a narrow set of packages and break other functionality of the same underlying distro. This is bad.
If you distribute a whole distro it is expected that everything works, like it is the case with Debian or Ubuntu. It might produce a bad image of Linux as perceived by new users when they realize that many things of this distro do not work at all. This is not the quality delivered by other Linux distros, so it is doing a bad job in representing Linux.
At least they should explain that on their website, e.g. "We deliver something we call a distro but this is not the same thing as you get from other people that deliver distros, we are only actively supporting one special desktop environment, but other things might not work as experienced with other distributions. We decided anyway to pretend we are releasing a whole Linux distro because..." (reason should be explained.)
I hope this was better explained. I still totally respect the work they put into it and I am thankful that a company is doing this at all, but they are distributing their software in a bad way.
Also luks and btrfs are good enough, and in-tree. They might not be as fancy as ZFS, but it's a better choice to use as default as they're standard and widespread.