I’m not sure if you switched from v6 to v7, or just generated a project in v7. I’ll detail both just in case:
Switched from v6 to v7
As stated here, models.sequelize will not work anymore, and should be replaced by something you should have configured. You can debug this by logging models.connections, or directly try models.connections.default instead of models.sequelize if you used the default models/index.js file provided in the documentation link I mentionned earlier.
Directly generate a project in v7 (With a single database connected to your backend)
You should be able to make models.connections.default work out of the box. Let me know if that’s not the case.
Just to be sure, I still did a quick test on my end, which works as you can see here
For a bit of context, this changes was introduced recently to ease the configuration of multiple database setup, and models.connections will contains all the connections made to multiple database, allowing you to select (from code) on which database you want to do your query.
In the meantime I’ll forward this in order to update the documentation of smart collections.
To also add context, I updated to V7 using a diff between my install and a fresh generated install because the upgrade documentation you mention is incomplete (missing to mention some files).