According to
https://developers.google.com/web/updates/2015/12/getting-started-pwa
a site must have been visited at least twice.
So maybe that's the reason it wasn't working for you immediately...

Unfortunately, the pwa specs are not 100% clear, hence leaving enough details to be implemented this or that way in different browsers.

So, for no apparent reason, (as I have not attempted to click the green button in a few days), as I launch Samsung internet this evening a notice pops up asking if I want to install an app and it has my site name associated.
I allowed and it installed remaining my saved information for login. It didn't install as a homescreen shortcut, but as an app and can be found in the app listing. Anyone know how this may have happened??
While I am somewhat confused, I am glad that it worked, would love to reproduce (nothing for Chrome yet) for users.
All features seem to work.

Thanks for the info Z.
Update on Firefox.
It only works if I am logged in on the browser before launching pwa.

John,
I found some similar reports on the web like
https://forum.developer.samsung.com/t/how-to-detect-if-pwa-is-installed/5798

Basiscally, with the Favicons and ServiceWorker installed, we have all necessary pre-requisites in place.
Thus, if some browser brands don't support it - we can't help.

You may try a different way to get that icon installed as described here:
https://superpwa.com/doc/test-pwa-samsung-internet-browser/

Working great with Firefox on Android pop-up shows and creates icon but not so much on Chrome or Samsung internet.
Those both show green button but nothing happens when tapped.
Anyone else??
Thanks,,,,
John.

Yes, as mentioned in the component description above.

Not compatible with Macs so I can't test it on mine to see how well it might work.

ill have to get back to you on this, sorry for ;late reply ., lots to do this end, but as soon as i can ill try and see if its an issue with other components and or custom components

Hi James,
meanwhile I managed to install Peppermint on an old laptop of mine with
Version 85.0.4183.83 (Official Build) Built on Ubuntu , running on Peppermint 10 (64-bit)
And I'm not able to reproduce your issue. The green button is working, and alternatively you may click the litte '+' icon in chromiums topbar. Both give

And after clicking 'Install' I got my icon on the desktop and the app:

Don't know what's different at your side. And besides that, I can't do anything inside my component except making the basic pre-requisites for webapps available. The rest is native communication between Chromium and the underlying window manager of the operating system.

yes sorry , here is more info . hope this helps. the about chromium options shows the following information ''Version 84.0.4147.105 (Official Build) Built on Ubuntu , running on Peppermint 10 (64-bit)''