First, talk to your vet.
Second, in general, grains aren't a problem for cats. As long as they're getting sufficient protein, some grain or other stuff isn't necessarily bad. If your cat has a problem with something, of course avoid it. But mine eat grass and drink from mud puddles when cat food and clean water is provided.
Making your own cat food sounds great, but you need to be very careful that you're providing a balanced diet. If what you're making is missing essential vitamins, minerals, or amino acids, then your cat is going to have a problem as some point. Plus, there's the extra effort involved (time is money!), and risk of spoiled foods/food poisoning. Making your own food is a lot of work to do it right, and if you don't, then the animal suffers.
Next, if you buy commercially prepared food, do some research into what kinds of issues they've had. I'm on the FB groups that get all the recalls, and I keep seeing recalls for all the "fancy" brands - not Iams, not Purina, not Science Diet, etc. Blue? Yep. Natural Balance? Yep. Plenty of others that I don't remember. Some of those recalls have been because animals died or had serious illnesses. So do your research.
You want to also find out if your food of choice has done feeding trials. Basically, they've done studies of animals fed exclusively that food and tracked how they've done. If they've done a study, awesome, what were the results? If they haven't done a study, ok. But you need to dig into it a bit more.
Bottom line - fads aren't good. For people or animals. You figure out what is affordable, what you can manage, they like, they do well on, and go with it. And when things change, you figure it out. And it will change. They just have live long enough. And when you're in the vet, you run it by them. A lot of vets won't directly say yes or no, so watch for the subtle signs of approval/disapproval. Ask them what they feed their animals!
Personally, I feed my cats Purina ProPlan, whatever the one for 11+ is (I have 19 yo and 10yo females). They get a variety of ProPlan and Neutro wet foods. I have trouble feeding the 19 yo now, so she gets what she will eat and thank goodness the 10yo is willing to go with it. Last year I had to do 100% food switches, and it's looking like I'll have to do the wet food again soon. Is it ideal? No. But when you're in your 90's (human equivalent), you can eat whatever you please. Vet is happy with ProPlan, seems not so thrilled with Neutro but understands my challenge.
In the past, I've fed Iams, Purina One, Blue, Royal Canin, Fancy Feast, and probably more I'm forgetting. Blue caused gas. Royal Canin got rejected after a while (taste). Iams changed formula or the store stopped carrying it, I don't remember. Purina One they aged out of (started causing digestive problems). Fancy Feast was rejected overnight for unknown reasons and nearly caused a health crisis (silly cat stopped eating).
Oh, if you even consider a vegetarian or vegan diet for cats - NO. Cats are obligate carnivores. If they don't eat meat, they will be malnourished. That is animal abuse. Dogs you can work around it. Cats you cannot. Either suck it up and feed appropriately or rehome the cat. (that's my PSA, because there are idiots out there. I'm not saying you are one)