This has been a frustrating issue for me for many years. The viewports in Layout will simply not export as DWG. Only the linework actually created in Layout will export.
Drawing as PDFs should look like this:
Export to DWG looks like this:
Version 10.15.1 (19B2106)
MacBook Pro (16-inch, 2019) Processor 2.6 GHz 6-Core Intel Core i7 Memory 16 GB 2667 MHz OOR4 Startup Disk Macintosh HO
Graphics AMO Radeon Pro 5300M 4 GB Intel UHO Graphics 630 1536 MB