I'm having a similar problem. I got a new computer Friday. It had Libre pre-installed and I installed Zotero yesterday. In tools>add-ons integration is enabled. In preferences>cite if I click Install Libre add on there is just a blank list. If I try manual installation the directory it sends me to (snap/zotero-snap/14) is completely empty. I don't have a ~./zotero folder and can't find extensions.json anywhere otherwise I would try deleting it. Since it is a brand new zotero install from yesterday re-installing again doesn't seem like it will work. Is there somewhere I can just download the integration.oxt file? I'm not sure what else to try.
Same here, my zotero plugin stopped working after the upgrade to libreoffice-6.4.4.2-snap1. I can install the zotero plugin via Snap Package, but nothing appears in LibreOffice. Last time it worked to uninstall and reinstall Libreoffice and Zotero.
I solved my issue by replacing the snap package of LO with the version from apt (6.0.7-0ubuntu0.18.04.10). Seems like libreoffice-6.4.4.2-snap1 is not able to access zotero out of his sandbox...
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The package maintainer, @extraymond, may be able to help.
I can install the zotero plugin via Snap Package, but nothing appears in LibreOffice. Last time it worked to uninstall and reinstall Libreoffice and Zotero.