Are Outdated Ecommerce plugins compatible with the Javascript Tracker v4?

Yes! While migrating to the current Ecommerce plugin is highly recommended, the old ecommerce events are still compatible with the new tracke.

You will need to add an overrides (see npm overrides for more info) property to your package.json as below. This will ensure there are no dependency conflicts:

"overrides": {
    "@snowplow/browser-plugin-ecommerce": {
      "@snowplow/browser-tracker": "~4.0.1"
    }