OK , a little more looking into this problem.
OpenCPN Chart Downloader is no longer officially supported on XP due to upgrades in many chart source TLS (https) security
policies. These new protocols are simply not available on XP. We all knew that this time was coming, and now it is here.
For some chart sources, it may be possible to use the chartdldr_pi.dll file from a previous release of OpenCPN, for example Version 4.8.4. Some sources have not yet updated their TLS configuration, and may still work
with the older protocols.
If you would like to try this, simply get and install a copy of OCPN 4.8.4, and copy the older chartdldr_pi.dll file over the same file in your new 4.8.6 installation
at directory "plugins".
Or stay with O4.8.4 on your XP machine, and use the chart sources that you find compatible.