today I am update ZH OSM Map from version 7.xxx to 8.22.xxx and and now is conflict with name of class plgZhOSMMapPlacemarksHelper
Fatal error: Cannot declare class plgZhOSMMapPlacemarksHelper, because the name is already in use in /mnt/web-data1/sedmicka_org/public_html/meteo/plugins/content/plgzhosmmap/helpers/placemarks.php on line 15
I think it is due to conflict of 2 versions of extension - J3 and J4
Today there are only simple parts: component, plugin, module and template
You need to uninstall Overview maps (for article and k2)
Here image, what you need uninstall - modules and plugins didn't contain any data, you can uninstall it
This error is conflict with plugin 2.x version. You can disable and will work. But you need uninstall, because there is no support for Overview maps, moreover, plugins have the other names - due to problem of naming extensions (plugin can't correct work is it name like plg_ , and my J3 names was like that).