If you use ADFS authentication in Power Platform, you might “not” be able to create Office365 connection using a different account other than the currently login account via the normal way. When select “Use another account” option, after enter the second account email in the login prompt, it does not ask for password and automatically create the connection using your current login instead.
The workaround is when the login prompt Window pop up, instead of enter the account details, copy the URL from the login address bar and paste the URL into Notepad. Search for “prompt” and replace the value assigned to it (more likely will be “select_account”) to be “login”. So instead of “prompt=select_account”, it will be “prompt=login”. Copy the modified URL and paste into a new browser window and complete the sign in process. After that sign in success, go back to create the O365 connection and pick the account shown on the cached accounts list.