It works if I set up one using the Aol autoconfiguration and the second with 'Other Mail Account'. I have just found that Mail stopped working for a second Aol account that I have. Now they show only 'aol.com' domain names. They used to support 'aim.com' domain names for the servers. The help page makes a point of stating that 'Only' the settings shown should be used.
If you want to see how the servers and settings are configured, it is easier to add the account using 'Other Mail Account' and filling in the details manually from the settings help page on Aol Mail web page. If you choose the Aol account type when adding, Mail finds and automatically configures the servers according to Aol's published settings which might have been updated since you originally set up your Aol account. Keychain Access is a macOS app that stores your passwords and account information and reduces the number of passwords you have to remember and manage. I have fixed problems like that by removing and re-adding the Aol account. If you have had your Aol Mail account setup for a while, it might have some old servers or port numbers in the setup.
