A recent episode of The Startup Ideas Podcast…
- 5 $1M+ startup ideas you can launch tomorrow with $0…
The first idea is to start a Canva agency 
Canva is a graphic design tool that 100M+ people use but few use really well.
The blueprint they lay out in the podcast…
• Create tutorials on how to use Canva
• Build an audience through YouTube
• Offer design services to viewers
• Hire offshore talent for execution
• Monetize through ads, affiliate links, and services
• Potential: $80K/month with 80% margins
Strikes me that the same blueprint could work for any popular software.
Others with 100M+ users 
- Notion
- HubSpot
- Shopify
- Airtable
- Figma