I love reading about recipe fails like this as much as the next home cook, but seriously, y'all. Before you can substitute something in cooking, you have to understand what it's actually doing in the recipe. You can look up 'egg substitution' and get a whole list of things, but whether it will be a successful sub depends on if it is replacing the original ingredient's job, not just its general characteristics. There are recipes where a mashed banana actually does work instead of egg. I've done it. Custard is not going to be one of those recipes. Usually the failure comes because people think in dietary terms when they should be thinking about function. In a recipe where egg is primarily providing support and stability, you have to look for a sub that will provide support and stability. Sometimes it's not a 1-1 sub. A powdered sub might provide the stability, but egg also is adding to the moisture content, which you'll have to take into account and add in another form. Replacing a protein with another protein only works when the presence of protein is important, like if another ingredient is acting on it to Do a Chemistry. You can't just look up a list of subs and pick whatever you like best/have on hand. You have to understand the sciency-part. Depending on what you are making, that part can be really really important. There are some ingredients with unique properties that cannot me subbed in certain recipes because the recipes are capitalizing on that ingredient's unique properties. Replacing those ingredients sometimes requires so much work and so many special substitutions, you're not really making the same thing in the end and it's just not worth the effort. Sometimes, you just don't get to have The Thing.
I'm poor and allergic to a lot of stuff, so I've had many substituting adventures, some more successful than others. My mother and I are diabetic, so while we're not doing hardcore keto, keto recipes provide us with safer-for-us options sometimes. But my mom is newer to keto than I am and is still in that stage where she's trying to make 'keto versions' of very not keto friendly things and is spending a lot of time and money on it. And I've had to just gently lay a hand on her arm and whisper, 'Momma, you're just going to have to do without. It's not worth it.'
Stop leaving comments or negative reviews on recipes where you change the fundamental ingredients. That's not a failure on the recipe's part, it's a failure on yours.
Your best bet is to learn how to cook, not just how to make recipes. There is a difference. When you understand what you're doing and why, changing things up becomes soooo much easier. And potentially saves you a lot of time and money and frustration when you can tell at a glance that, 'Yeah, I'm not going to me able to make that work. I just can't have that.'