Release notes for 7.2 says that it's now possible to create "an array or single device pool" with ext4 formatted drives:

I'm curious about the "single device pool" wording. Does this mean, I can't create a pool consisting of multiple ext4 drives?
Is there a way to combine multiple ext4 drives to a storage volume similar to a Logical Volume Management (LVM) solution?

No - only single devices are supported. What it saying is that if a disks is already formatted in one of the listed formats then it can be used in Unraid. In addition you can format new drives in Unraid to ext4/ntfs, but not to ext2/ext3.

Note that in the main Unraid array although each drive is a single file system you can have User Shares that span multiple drives (even if they are not all the same format) as the User Shares system is independent of the underlying file system formats.

4 hours ago, itimpi said:

Note that in the main Unraid array although each drive is a single file system you can have User Shares that span multiple drives (even if they are not all the same format) as the User Shares system is independent of the underlying file system formats.

Can User Shares span multiple pools or unassigned devices as well? Or are they limited to the classic Array setup?

Just now, TOMillr-old said:

Can User Shares span multiple pools or unassigned devices as well? Or are they limited to the classic Array setup?

User shares are not available on Unassigned Devices.

User shares can exist on pools, but not span multiple pools directly. For pools this is not normally an issue as pools can inherently be multi-drive. Having said that any pool can be used for ‘caching’ new files for a User Share regardless of where the main body of the User Share is located.