Thank you for posting this in Microsoft Q&A.
Microsoft defender for endpoint is part of Microsoft 365 Defender. Or you can also get Defender for endpoint as separate service plan.
However, defender for endpoint service plan is not part of Microsoft 365 E3 license pack.
Microsoft 365 defender is part of Office E5 plan, and as I mentioned above, Microsoft defender for endpoint is part of Microsoft 365 Defender.
If you have Office E5 license, then you will by default have Microsoft defender for endpoint.
Let me know if you have any further questions.
Please "Accept the answer" if the information helped you. This will help us and others in the community as well.