You should be able to set up the Elements Editor for external editing in Lightroom preferences. But there will be a camera raw incompatibility as LR6 is now quite old. When editing from Lightroom simply click render using lightroom or open anyway.
Thanks for your answer. I'll try it tonight.
I had understood that you wanted to know if there is way to convert LR catalogs into PSE catalogs (the reverse of what is available to convert PSE catalogs for LR). Am I wrong? The answer is no.
Or do you want to know how best to migrate completely from LR6 to PSE?
No, I wanted to edit my photos on the notebook in Lightroom 6, and then continue editing in Photoshop Elements. For this you need a plugin, and then I asked.
Greetings from Berlin