This is due to pre-2017 versions of SketchUp installer setting the BROWSER_EMULATION registry attribute for "sketchup.exe" in the MSIE Feature Controls to IE version 9 emulation.
Google Maps no longer supports any IE version or emulation below v 10, and so is displaying this warning.
Temporarily you may be able to dismiss the warning and use the webdialog anyway,... but this may only be a temporary workaround that Google Maps may switch off.
There are two long term solutions:
(1) Set this registry attribute to IE v 11 emulation (as the SketchUp 2017 installers do.)
(2) ... or for an extension (plugin) to use a meta tag in it's html
<head> element for the WebDialog.
[ This has been recommended for years ! ]
AND use a
<!DOCTYPE> directive to prevent Quirks mode!
<meta http-equiv="x-ua-compatible" content="IE=11">
... or for just the latest version:
<meta http-equiv="x-ua-compatible" content="IE=edge">
See for reference: