Hi @Elias Markelis , thank you for posting in the Q&A forum.
You will need to migrate Office 365 E3 developer sandbox subscriptions to Microsoft 365 E5 with a new tenant, by deleting your current subscription and replace it with Microsoft 365 E5 developer subscription.
Please refer to the document here for detailed steps for the migration: Migrate from Office 365 E3 to Microsoft 365 E5.
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