Having the same issue with Samsung Galaxy TAB A 2019 and witnessing the crap support from Viber, I would like to point that the issue is indeed caused by the Viber device identification from screen resolution as Robert suggested. What is important is to differentiate screen resolution to one that can be identified as "tablet". In an Android developers site I found the following dp info:
Here's how other smallest width values correspond to typical screen sizes
320dp: a typical phone screen (240x320 ldpi, 320x480 mdpi, 480x800 hdpi, etc).
480dp: a large phone screen ~5" (480x800 mdpi).
600dp: a 7xe2x80x9d tablet (600x1024 mdpi).
720dp: a 10xe2x80x9d tablet (720x1280 mdpi, 800x1280 mdpi, etc).
For some reason my tablet had as factory default setting minimum width 533 dp! On Android 10 you have to dig deep to find this by activating Developer Options menu (Settings/About tablet/Software Information/7 taps on Build Label) and under Drawing label find the Minimum width setting. For a 10.1'' you can set it to 800 dp. After restart the installation as secondary device proceeds as normal.
I have to point that Viber support after passing them a slum dunk with the post from this forum and my minimum width setting did not even bother to look for an answer!! They sent me as a reply the summary of this post with the "recommendation" to find View and Small Screen setting on Android !! I hope that my recommendation to include a warning to their knowledge base (which kept sending me as a fix to this problem !!) would resolve future issues. Especially since it is so easy for a developer/ technical person from a multi million dollar company to spot and solve.
Thanks for the info provided by Robert and Fendonkadifeli!!