Maximize Compatibility not working for me in PS 2020 classic

I beg to differ with some statements made in this thread- but if others see differently I can only suggest that there are differences between Macs and PCs (and earlier Lr versions!), and I seldom make complicated or extreme edits in Ps.

For clarity- when you are re-opening a TIFF/PSD file created from a raw file in Lightroom-Classic, the TIFF/PSD is always the “ORIGINAL”.  “Original” in this context no longer refers to the first RAW file that was sent to Photoshop. This is an important point to understand.

“Only with the Edit Original will you get the layers.”

“..if you Send a COPY of it (-the TIFF/PSD ‘Original’) back to Ps then all layers are Flattened in the COPY that is made.”

False.

Both options in the [Edit In] dialog- “Edit a Copy” and “Edit Original” will preserve the layers in Ps.

(Read the fine print in the dialog)

“IF you apply ANY edits from LR to a layered image, it must be flattened to apply said LR edits just to then render and open that data (the Lr edits) in Photoshop.”

True (to SEE the Lr edits in Photoshop).

 However, two situations can occur-

1) If you re-open the layered file by [Edit Original]- you will not see the Lr edits applied, but the Lr edits are re-applied when the file returns to Lightroom. AND the Lr edit History is preserved.

2) If you re-open the layered file by [Edit a Copy]- you will not see the Lr edits applied, but the Lr edits are re-applied when the file returns to Lightroom. Lr edit History is lost.

Eg. In Lr I applied a B&W treatment to a colored TIFF file (edited in Ps with Hue & Text layers)-

 [Edit a Copy]  (Lightroom edits will not be visible)

 The layered file in Ps does not show the Lr B&W edit. I added more text in Ps-

 The file when it returns to Lr has the B&W edit re-applied -

So, in PS the layers can exist, but in LrC they will not show up individually, instead will act as a flattened image.

see:

https://lightroomkillertips.com/lightroom-handles-layered-photoshop-files/

To add (and maybe additionally clarify) to what was stated: IF you apply ANY edits from LR to a layered image, it must be flattened to apply said LR edits just to then render and open that data in Photoshop. If you select Edit original, LR simply hands off that original with the layers. Hand off anything (layered or not) that has LR edits,  a new rendered iteration is created and sent to Photoshop; without layers. Because as stated, LR doesn't support layers (with it's edits). 

Lightroom does not support layers at all. This is the downside of a mixed workflow, and personally I prefer to stick with Photoshop for RGB files and Lightroom for raw files. For exactly this reason.

To work this way, you need a very disciplined workflow and thorough understanding of all the underlying mechanisms. See here (scroll down to the last four posts): https://community.adobe.com/t5/photoshop/colour-not-matching-photoshop-to-lightroom/m-p/11408771?page=1 

What option are you selecting in the Open dialog box when sending to Ps?

Edit a Copy w/LrC adjustments?

Edit a Copy?

Edit Original?

Only with the Edit Original will you get the layers. The other 2 options are kind of Self Explanatory, Edit A COPY

The copy of the image file will be a Flattened version.