Thanks, it was quite hidden from the sight, how to get to the instructions.

For others looking for the same, it here: https://docs.microsoft.com/en-us/visualstudio/mac/create-off...

(You can get there from the linked page, click Release Notes, then Downloads link in the third paragraph, then "How to install offline" at the bottom, just above the fold.)

And the offline media build failed, just after 18GB download:

    [Exception] System.AggregateException: One or more errors occurred. ---> System.IO.FileNotFoundException: /Users/<username>/Library/Caches/XamarinInstaller/Universal/downloads/repository-10.xml does not exist

That looks like maybe you installed in the wrong order? Seemed to work ok for me.

How in the wrong order? Exactly as described on the page.

There is not much wiggle room, launch the installer with the switches, select a directory where to build the installer, go. There's not much that you can reorder.

Of course, on the second try, although the downloader caches whatever it downloads, it does not use that for the next round, it will throw it away and redownload everything. So 36 GB of traffic later, I gave up.

Oh I see, you found yet another set of instructions. I meant these: start the regular installer, pick manual installation from the app menu, it gives you a readme with direct download links. Download the components you want (none seem to add up to 18 gb, for me at least), install and run.