I have switched off and on iCloud and sync on both Mac and iPhone, restarted both etc. I have tried all tricks and tips but still the newer photos don't show in Photos on the Mac.
Mike, the switching on and off may be the reason, why the updating never finishes.
When you turn iCloud Photos off and then enable it again, iCloud Photos will start a new upload to iCloud and merge the complete library again into the existing library. You will just have to wait longer.
Your new photos will start downloading from iCloud to your Mac, once the new upload has finished.
But Catalina has brought an added complication. There may be photos in your library, that are not compatible any longer with Photos on Catalina. You have to identify any video or image, that is an unsupported format and cannot be processed any longer by Photos. These items need to bereaved from your Photos Library and converted to a compatible format. Look for old videos or PDF files, or audio files.
And check the status of the upload to iCloud. Search for references files or files "unable to upload" with smart albums as described here: About the status bar in Photos for macOS - Apple Support