I can't remove the email adress of around the same age. I've found another user with the same problem https://www.cnet.com/forums/discussions/how-to-remove-recovery-email-from-yahoo-mail/.
It looks like the only options left are support or delete the account.
No way for top contact.
But you can delete a contact, via Contacts icon (top right, near 15 icon), click on contact, click on ... (more contact options); then Delete and OK confirmation. Need Sign out.
For Suggested Searches is more simple. Just click the X in the right of Suggested Searches list. That suggested search will be replaced with another.
The mailbox gets de-activated - by that, all emails in your mailbox are deleted. The next time you login, the de-activated mailbox is re-activated and you start from scratch. Deletion implies that your account is wiped out and you need to re-register. However, that is not the case