Line appears on the screen

I have Audacity 2.2.1 and already installed 2.3.3, on Linux Mint 19.3.
And whenever I open it, a line appears on the screen.
What bug is this?

No idea. It does not happen for me on Xubuntu with Audacity 2.2.1 or 2.3.3.

Is the line attached to the track?
Does it move when you move the Audacity window?
Does the line appear in exactly the same place each time?

Do you mean that the problem didn’t occur with Audacity 2.2.1, but does happen after updating to 2.3.3?