To continue using Manifest V2 extensions:
- Go to: chrome://flags/
- Search for "mv2"
- Set "Allow legacy extension manifest versions" to Enabled and the 3 others to Disabled:
- "Extension Manifest V2 Deprecation Warning Stage"
- "Extension Manifest V2 Deprecation Disabled Stage"
- "Extension Manifest V2 Deprecation Unsupported Stage"