Pardon the delay here. Some updates/replies:
This didn’t change anything, so that rules out possible browser issues
A bit of a historical context.
I wanted use Google Sheets (GS) as the primary data source because my customers need full access to their data and they’re already used to Sheets. But I encountered this limitation about Glide data sources: we can’t connect an existing Glide table to a GSheet yet. So these are the steps I took instead:
- Copy Inventory by Glide template into a new project
- Copy all the Glide Tables (“GT”) in the template into a Google Sheet (basic fields only), each table onto a separate sheet on the same file
- Add a row ID column on the tables that were missing to ease relation lookups
- Make the GSheet file the primary data source for my project
- In the new data source, recreate the relations and other computed fields to match the old template project, doing any other customizations as necessary
- Replace each GT with each sheet in the GSheet doc
- Remove the old GTs after testing the layout
Everything generally went well, except step 6 had caused problems for the Inventory tab: it made the Inventory create screen to “disappear”, similar to what’s described in Layout disappears when you reselect a tab's source sheet. The layout components of the tab were being shown, but the create form itself was not being rendered when clicking the add button. It turns out that the Inventory layout’s Source has been set to the GT “Inventory”. I only got to find out about this when I deleted the GT sheet, and Glide automatically switched to the GSheets table of the same name. Setting the Source of the tab layout to the GSheets table fixed this problem.
Yup, this is what I ended up doing.
This would have been great - or better yet, to have the ability to re-use forms 
- but copy-pasting (both cross and intra-project) didn’t work for me reliably. It only works for the first component and then Glide’s clipboard doesn’t seem to updated, all subsequent copying just pasted the first component in the source projects.
All in all, this is how my ‘inlined’ form from the “Restock” action now looks like:
