There should be (sort of) multiple file systems on a LVM block. This is the way a physical file system is represented in LVM (at least as far as LVM and LVM2 are concerned).
If you look at the fs with Gparted GUI, it will look different than other partitions. Whereas most partitions will be represented by a bunch of blocks laid out in a row which represents a drive, the LVM partition will be 2 blocks, one stacked on top of the other, nested within the row.
This is because LVM consists of multiple volumes, which work together to store, and give you access to, your data. Sort of like RAID, although here is where their similarities end.
And this is where it may get a bit confusing. Technically, these two drives are representing the same data, but in different ways. If you are familiar with archiving, the same abstraction can be made to work for LVM (although the terms are not interchangeable.)
LVM has logical volumes (LVs), physical volumes (PVs), and volume groups (VGs). A single volume group can hold multiple physical volumes. It will also contain a logical volume, which holds metadata for the physical volumes. In other words, it is said that the logical volume in a VG 'maps' the VG's physical volumes. This metadata is why I compared earlier to the concept of an archive.
This mapping functionality gives LVM some advantages over other file systems. For one thing, since its physical portion can be split into portions, the LVM partition, itself, can be split across more than one drive. This is not possible with, for example, Ext2,3,4 volumes.
The main disadvantage of LVM (at least in my experience) occurs in the 'applied' realm. Especially where Ubuntu is concerned.
For example, if you obtained your LVM via the "repair drive" option on the Ubuntu Live media (i.e. you used a USB boot stick to repair a broken partition, and got back a LVM2 / LUKs partition), then their is a high likelihood that it will not work.
Disclaimer: This is intended to be a very high level explanation, not a deep dive. In that regard, some of the statements are in a "more or less" format, so as to make the concepts understandable. In some places, I actually started to explain more deeply, but found the result to be hard to follow, so I changed them. For a deeper look, see here.
TO ANSWER THE QUESTION ITSELF
The filesystem itself is only a piece of your lvm partition. In each instance I have seen so far, in a LVM partition created by Ubuntu Live, there are 2 PVs. This may be editable. That said, I have worked with 5 separate blocks, all created by different users at different times and on different machines, and in my experience, 2 has always been the magic number. Take that however you want.
The best way to see the concept for yourself (on 20.04; not sure about the Gparted version) is to inspect your drive with Gparted GUI. You will see the abstraction I've laid out first hand.