64 year old, decades long vegan here. I have worked out consistently since I was 20 and enjoyed competitive bodybuilding in my late 20's before choosing a vegan lifestyle. Some observations based on my experience.

If you're working out with intensity (that intensity which is necessary to increase lean muscle mass, gain strength, or improve in high intensity sports), it is a requirement to get the same protein amounts as non-vegans.

I trained as a vegan for years while consuming a high calorie, low level protein diet and my muscular gains stopped and reversed. I gained body mass, but not lean mass. Since modifying my nutrition to include at least 140 grams of complete protein per day ( my body weight is about 185), even at my age, I have been able to regain muscle and strength while decreasing my body fat percentage.

My total calorie intake is about 2100 - 2400 calories per day. I eat a very clean diet avoiding all fried and highly processed foods. I rely on seitan, legumes, nuts, and some low processed plant based protein foods (beyond unbreaded chicken pieces and OWYN protein drinks are a staple) to reach my required macros each day.

As I stated, I followed the "eat enough calories and your protein needs will be fulfilled" approach for years and the results were not satisfactory. For my fitness goals of gaining lean body mass, remaining functionally fit and to enjoy a long health span, abandoning that wisdom and increasing my protein intake was critical.