Please, I am interested only in the disadvantages of replacing meat with mycelium
https://www.foodnavigator-usa.com/Article/2022/07/21/meat-from-mycelium-fungi-fueled-meati-foods-raises-150m-to-make-holy-grail-of-alt-meat-whole-cuts there are a few articles I can find. https://scholar.google.com/scholar?q=mycelium+meat+science+review&hl=en&as_sdt=0&as_vis=1&oi=scholart#d=gs_qabs&t=1670859285686&u=%23p%3D1wPEFDmF80EJ try scholar.google.com
Other then what has already been mentioned protein is also a problem. Beyond mushrooms being a poor protein source they are also not balanced (and plant protein in general has the same problem).
When you digest proteins your body ultimately breaks that down a couple of times until it reaches individual amino acids. There are 9 essential amino acids (plus two that are almost as important) and there is no plant (or mushroom) based protein source that contains all of them (in quantities that its possible to eat, you have to eat 10kg a day of mushrooms to hit protein targets and you would die maintaining that diet) vs animal meat that nearly always contains all of them. Its possible to supplement and ensure you eat lots of seeds (inc. legumes) but if you are relying on supplements instead of a balanced diet you are generally not doing nutrition right.
If you don’t want to eat walking animals there are lots of other options. Fish is a great option (often more nutrient dense then beef/chicken) and its not very difficult to avoid mercury.