Linking PS Elements 2021 to Premiere Elements 2018

As I said before, you cannot link one version of Photoshop Elements with a different version of Premiere Elements.  So your Welcome/Home Screen for Photoshop Elements 2021 will only link to Premiere Elements 2021 - which is not installed on your machine.  That is why you get the message to start a free trial for it, even though you do have an earlier version of Premiere Elements (2018).  There ae a number of reasons why this is the case.  The Organizer uses a different format each year, so you can't share the Elements 2021 Organizer with the 2018 version.  Other changes are often made between versions such as the supported video formats.  For example, the High Efficiency Video Coding (HEVC) format has only been supported in Windows Elements for the past few versions.

Since you have different versions of PSE and PRE, you also have two versions of your Organizer catalog.  It is somewhat difficult to keep these in sync.

No version of Elements has been able to link different versions of Photoshop Elements and Premiere Elements.  However, you can open both programs and click-and-drag a video thumbnail from the Organizer to Premiere Elements for editing.