I too am in the M Mode boat. Since the introduction of digital cameras, I shoot manual 95% of the time.
Reason being is that I was never able to get constantly correct exposure from my Canon DSLR bodies. For years I felt Nikon bodies made a much better job in this regard. The first Canon camera that worked for me was the 5D III, but by then I was so used to shooting manual that I simply forgot to use another mode. But when I used it, it felt very convenient

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However, I don´t want to think during a shooting whether a scene needs spot metering or center weighed, matrix whatever. I feel that takes too much of my attention. I rather concentrate on framing and on the expression of the people in the shot.
Also I never felt spot metering was quicker than manual because most of the time I shoot within the same lighting situation for quite some time and using spot metering for every single shot took more of my time than dialing in the correct exposure once and then shoot away. When I shoot in changing lighting situation, I usually have the time to adjust the settings accordingly.
Today many cameras show if your exposure is off. Even in manual mode you get the EV +/- reading in the display - so that might help in case you want to shoot manual for whatever reason. But if your camera doesn´t meter correct, that will only give you a ball park.
But as many others said it is not that M will show that you are a pro and everything else is amateurish. It is the result that counts, however you achieve it. You can get the same image with many modes. Choose what works best for you and if you have time, experience a bit with different modes to see wether there is a mode that works even better for you.
Beside that: I never felt that it was desireable to look like a pro or being called a pro. Nowadays I even use tiny mirrorless cameras for client work. All I want is to like my own images and if I like my images, the client will like it too

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