Can't drag Lightning Web Component onto default Home page in Lightning App Builder

Title: Can't drag Lightning Web Component onto default Home page in Lightning App Builder (Quick Start: LWC) 

Content: 

I've successfully created and deployed a "helloWorld" Lightning Web Component (isExposed=true, targets set for AppPage and HomePage). Deployment succeeded via SFDX. 

Now I need to add it to the default Home page ("Seller Home") via Lightning App Builder, but I cannot drag the component from the Components panel onto the page canvas. I've tried: 

• Dragging directly (mouse down, move, release) — doesn't drop anywhere on the page
• Zooming out the browser to avoid scroll-during-drag issues
• Keyboard-based drag (Tab + Enter/Space + Arrow keys)
• Looking for a "+" insertion icon on hover — none appears
• Creating a brand new App Page instead (worked fine there, easy to drag onto blank canvas) — but the challenge specifically requires it on the "default Home page," and error says: "Make sure you add the 'helloWorld' Lightning web component to the default Home page."

My Home page ("Seller Home") uses a fixed multi-column template (Close Deals / Plan My Accounts / Grow Relationships / Build Pipeline / My Goals / Today's Events / Today's Tasks / Recent Records / Salesblazer) with no visible empty drop zone. 

Is there a specific way to add a custom component to this "Seller Home" template, or should I be using a different (simpler) default Home page? Any help appreciated — I'm on Chrome, Windows.