Most extensions that are maintained by a third-party developer (i.e. that are not an Inkscape stock extension) need to be updated to work with this version of Inkscape. Inkscape contributors have contacted many extension authors already to let them know about the upcoming changes. If your favorite third-party extension still needs to be updated to be compatible with Inkscape 1.0, please point its author to [https://wiki.inkscape.org/wiki/index.php/Release_notes/1.0#For_extension_writers the section about updating one's extension in the Wiki].
Third-party extensions need to be updated to work with this version of Inkscape.