The "Microsoft 365" environment is a standard production environment that is created automatically when a user with a Copilot license uses features like scheduled prompts or recurring prompts for the first time. The "Microsoft 365 Copilot Chat" environment is specifically created when a Copilot-licensed user engages with Copilot Chat functionalities.
Both environments are managed by Power Platform and do not consume storage from your tenant's entitlement, meaning they won't appear on capacity pages.
As for removing these environments, yes, you can delete them through the Power Platform admin center. However, if a user uses the respective features again, the environments will be automatically recreated.
In summary, these environments are created automatically when certain features are used, and while they can be deleted, they will reappear if the features are used again.