[Qgis-user] how to update QGIS to latest version in Debian Linux (version stretch)

[wxgis]

As I am working in Debian Linux, I did "apt-get install qgis" so I could
start working with QGIS.  This installed an 'older' version of QGIS, 2.x (I
forget the suffix now).  Anyway, this seemed way too far back to be
practical so I checked how to upgrade one's QGIS version.  There is the
"Quickstart" guide, which one reaches after you start up QGIS, and link to
"Help -> Check GIS version".  There, one finds the link to get the "latest"
version, 3.16.5.  When you link there, one finds the "Quickstart" guide and
I went down to the section for "Debian/Ubuntu Linux".  Stepped through
everything:
1. apt-get install gnupg ...
2. wget -qO ...
3. chmod a+r ..qgis-archive.gpg
4. add-apt-repository "deb https://qgis.org/debian $(lsb_release -c -s)
main"
5. apt-get update
6. apt-get remove qgis (to clear out an older version)
6. apt-get install qgis qgis-plugin-grass

All worked fine, but the QGIS version it installed is 3.4, a great step up
from 2.x, but not the "latest" version, 3.16.5.  A further read indicates I
need to have the right lines "deb ..." and "deb-src ..." lines in the
/etc/apt/sources.list file, but need help in nailing this down.  (for
reference, I am in Debian Linux (version "stretch").  Will gleefully accept
any and all information.  TIA! 
--Steve





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