I'm new at this one too!
Basically you can select one or all the files and save to a chosen location and then import into (old) Lightroom Classic. How it works varies with file type and one selection in the Save To dialog. It is JPEG or Original+Settings.
With RAWs and "Original+Settings", you get the original and a xmp file. The two will Import into LR classic with the look of what you created.
With TIFFs and JPEGs it seems that edits from new LR will carry into the old LR but the sliders are reset to zero.
Hope this helps. You definitely can put photos back into old LR classic and the edit will be there but not necessarily recoverable.
I was wrong! A little more testing and I got better results!
"Save To" with "Original+Settings" does bring the edits and slider positions from (new) Lightroom CC to (old) Lightroom Classic for all three file types.
What confused me was that I was monitoring the progress in Windows Explorer and thumbnails all looked like originals. Once imported to Lightroom the images matched and the edit sliders were where they used to be.
There is also a days old new app from Adobe that may do what you want. It empties your cloud file and puts originals on you computer.
Read about it here: Download synced Lightroom photos and videos from the cloud to a computer