Update: I ran into this message, and didn't quite understand this responses above. Here's what I learned: The lynx STARTFILE is the 'home page' that you see if you don't specify a URL on the command line.
Older versions of lynx point to http://lynx.isc.org/ in the config file. Newer versions of lynx point to https://lynx.invisible-island.net/ (See the two config's below.)
To stop this message, update to a recent version of lynx or update the STARTFILE in the config file. I used brew update lynx on my Mac to get the newer version.
Older version of lynx
### Lynx 2.8.8rel.2, at Thu Jan 2 10:34:54 2020
STARTFILE:http://lynx.isc.org/
HELPFILE:http://lynx.isc.org/release/breakout/lynx_help/lynx_help_main.html
...
Newer version of lynx
### Lynx 2.8.9rel.1, at Thu Jan 2 10:43:33 2020
STARTFILE:https://lynx.invisible-island.net/
HELPFILE:https://lynx.invisible-island.net/lynx_help/lynx_help_main.html
...