Microsoft announced back in August 2021 that Microsoft Defender for Endpoint Plan 1 would be available in a couple of different ways (see our blog: https://bit.ly/3LsJmF5).
Here’s the update: in November 2021 it was made available as a separate SKU for use on up to 5 devices for $3 per user per month – this is the announcement with a useful chart comparing it to Plan 2: https://bit.ly/3u4quG7. And the second part of the plan came together in January 2022 with Defender for Endpoint Plan 1 now being automatically included in Microsoft 365 E3 licences, and you can find that announcement here: https://bit.ly/33VsPbN.