Wozu benötige ich das Grafikformat „.dng“?

In order to get all the options and the best quality, I photograph in "RAW" format.

After saving to pc, I convert the photo to "PSD" format. This is my master photo. The original "CR2" file will be deleted.

The editing is done in Lightroom and/or Photoshop. The formats ".tif" or ".jpg" serve for output (depending on the type of output). Why do I need the graphic format ".dng" because it is lossy?

Another question:

It happens that I can hardly decide whether the edited photo (variant A) should not be edited a little differently (variant B). So you convert both variants to ".tif". Unfortunately, the processing steps are no longer accessible.

If I get a better idea after some time, I have to repeat the complete editing (with one or two changes). This is sometimes very expensive.

How can I save the editing steps so that I can use them later?

Reply to quotes-

"I convert the photo to "PSD" format."

NOT a better "quality" than the raw CR2 (through Lightroom-Classic or ACR)!

Why do I need the graphic format ".dng"?

You do not need it!  If you KEEP the CR2 file you always have the best photo data.

(In Lr, You can Export to a DNG file as it will save editing metadata within the DNG so that you can share the DNG with other Adobe editors that will see your final edit that you made to the CR2 original camera photo.)

"The formats ".tif" or ".jpg" serve for output."

Consider these as BOTH "lossy" formats. Even the .tif loses some abilities of a raw file when converted to RGB pixel data.

"edited photo (variant A) ... edited a little differently {to} (variant B)"

Edit the raw CR2 and make VIRTUAL COPIES in Lr. Separate Editing History is recorded for both varients.

Summary-workflow in my opinion:

Keep the CR2 files.

Edit the CR2 and Virtual Copies.

Only export to a .tif (.psd) or .jpg when needed for a special use, or editing function is not available in Lightroom (or ACR).