18.04 – Can someone explain me what this is and how I stop it?

When you see a “change in progress” message it means that Snap is working on something in the background. You can get a list of what’s going on in the Terminal like this:

snap changes

If Snap does have something going on, then you’ll see a message like:

123  Doing   2021-05-06T00:00:00Z  -  Remove "opera" snap

Otherwise, you’ll see:

error: no changes found

If you need to abort a Snap change, you can do this:

sudo snap abort {ID}

Note: {ID} is found in the result of snap changes.