I never really use Mail & Calendar, because I need the Exchange and Microsoft 365 features of full Desktop Outlook. Desktop Outlook also tries to steer its users to the New Outlook, but New Outlook is largely USELESS compared to the classic Desktop Outlook. NONE of the power features of Desktop Outlook are included -- rules, macros, the powerful editor, auto-archiving, admin controls, etc. NONE of those work in the New Outlook.
Worse, at least this was still the case in my last check a couple of months ago, the editor broke with how ALL OTHER WINDOWS AND OFFICE editors work with spellcheck. In everything else, when Word or another program (even text fields in the browser) detect a spelling error, they red-underline. Then, you can right-click on the red-underlined word to select a replacement. Right-click did nothing on misspelled words in New Outlook (at last test). Instead, it wants you to left-click, which should just position the cursor (to be fair, I see Word has recently also started providing alternatives when left-clicking, but it also still supports the right-click for those of us who are used to that from the past 20 years of that being the consistent UI element).
Also, if you have a long list of folders that is longer than what fits in the window in just about everything else, when you drag over that last it will scroll automatically if you drag the item to the top or bottom, enabling you to reach all folders, including those that are not currently in view. In New Outlook, even this basic drag-and-drop didn't work, with nothing happening when dragging to top or bottom, meaning no way to reach those other folders. Instead, you have to scroll the folder list first, then pick up the item you want to drag, then drop it in the desired folder. WTF!?
This app seems far, far, far from being ready for general use. It's missing all the features that make Desktop Outlook a powerhouse and it's missing the basic UI features that every Windows app should have, and even lowly Mail & Calendar already does most of these right.
I generally support Microsoft's efforts, but I would rate New Outlook somewhere between a D- and an F. The only reason it could rise to a D- is because it does work to actually send and receive email, but it does less than all the alternatives.