is appleaccount@insidesupport.apple.com legitimate email address

Mine was @insideapple.apple.com as well, but in any case even if it is a legitimate email from Apple, you should still use safe internet practices by not responding to unsolicited emails by a link that requires you to enter personal information. All of the information provided in that email should be done by you initiating the action using the safe methods to access your account.

• To review account information

Manage and use your Apple Account - Apple Support

• To set up a Recovery Contact

Set up an account recovery contact - Apple Support

• To change your password

Change your Apple Account password - Apple Support

• To set up a Legacy Contact

How to add a Legacy Contact for your Apple Account - Apple Support

The one I received was from appleaccount@insideapple.apple.com and it is legitimate. It is about: "Let’s check up on your Apple Account."

(slightly different address than what you posted)