Step 1
Type MV2 in chrome://flags.

Step 2
Enable the flag #allow-legacy-mv2-extensions («Allow legacy extension manifest versions»).
Step 3
Disable the flags:
#extension-manifest-v2-deprecation-warning(«Extension Manifest V2 Deprecation Warning Stage»)#extension-manifest-v2-deprecation-disabled(«Extension Manifest V2 Deprecation Disabled Stage»)#extension-manifest-v2-deprecation-unsupported(«Extension Manifest V2 Deprecation Unsupported Stage»)
Step 4
Relaunch Chrome.