I don’t think it can conflict. Where Deck is a full app running on a Nextcloud instance, it appears that OpenProject is merely a status message connector for the NC Dashboard app.
See if your instance has the connector by opening your https://sd.fqdn.tld/index.php/settings/user/connected-accounts page.
For example, mine shows my Moodle and Twitter updates after I made the connection to those accounts active. I never added the OpenProject connector to my https://sd.fqdn.tld/index.php/settings/apps page because I’ve never used OpenProject yet.