Outlook365 problem

I have Microsoft 365, Under Outlook I have two accounts, Outlook.com and Gmail.com.au. When I start Outlook I get the message in the attachment, I also get a purple balloon under the Outlook icon in the Sys Tray, if I click on my gmail account the balloon disappears, I do not wish access my email in a browser, if I click NEXT Outlook just opens, not in a browser but in the stand-alone mode. and I can use it normally apart from not being able to send email from my Outlook.com account