Based on my knowledge, we cannot use the Exchange Hybrid Agent and classic hybrid at the same time. We have to choose one topology for Exchange configuration.
If you need other assistant about migration endpoints or mailboxes migration, you can post a new question in our platform with more details. Our support engineers and other platform members will pay attention to it. Additionally, here is a blog about Understanding Hybrid Migration Endpoints in Classic and Modern Hybrid, hope you can get some useful information from it.
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