Thanks both of Nuno and Salvstore.
Below are few findings after which everything cleared out.
1. I was able to add multiple mail accounts from support subscription
2. When tried adding account from myoffice subscription it was not giving any error message but was not proceeding further after adding account details.
3. All these activities were performed from open internet.
4. So I tried configuring outlook on a new vm and I got the error message that as machine is not joined to domain, I will not be allowed to configure outlook. (Conditional Access policy is blocking it)
5. So I went to on premises network removed all accounts and added primary one and then added secondary ones from support subscription, all works fine with individual profile and multiple accounts in same profile.
So it was nothing wrong in steps it was conditional access policy which was giving issues. What a bummer
😜.
Observation
1. Adding secondary account required open internet in my case
2. After adding secondary accounts I was able to Access shared folders etc however in more settings add additional accounts was grayed out.Though I am able access the auto mapped shared mailboxes.
Thanks all for your kind support, we can close this now.