I have an OSMac 10.12.6 Sierra and I can draw in 3D but cannot access 3D Warehouse. I cannot upgrade via Apple Store either.
The 3d warehouse and other web tools in sketchup are supported only by the last 3 versions.
to be correct, they are webpages encoded to work on the more recent versions of chromium, the browser inside SU.
the 3d warehouse isn’t supported by the in-application navigator anymore, not since 2020 ?
however you can still access it in your browser and download files there as collada.
sketchup was never sold in the apple store. Like most softwares, you can get it on their website, sketchup.com
When was the last time you tried to download a model from the 3D warehouse? It’s been some years since sketchup 2017 lost support for online services from the program, you may also notice that the extension warehouse and generate report features don’t work.
If you have a perpetual license you can’t upgrade like in the past, paying a fraction of the original price and get the latest release with a perpetual license, you’ll have to subscribe to an annual plan, if you don’t want to keep paying after a year you won’t be able to use the program at all.