Correction: It was when you are using the Online version of SU that you get the message when you try to download it. I am still able to browse the 3DW from there, open it into the web version of SU and click download and select the older version. I guess that I mistakenly thought it was when simply browsing the 3DW website (without starting from SU in the browser) that I got this message. So if you want to save to the a version older than 2019, you have to use the web version of SU to do it.
BTW Paul, I found a couple of your topics or blogs about your chevalet designs in lumberjocks and it looks like at least on the couple of the ones I looked at , the 3DW links are broken. Not sure if that is something that Trimble did, lumberjocks broke the links during the conversion or what. Not sure if you care if you plan to migrate things to here but I thought I would just let you know in case you refer your students there for any reason.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.