I'm a pellet girl Flakes are much harder for goldfish to eat. They're good when they're very small, but once they can fit a mini pellet in their mouth, that's a better option. I've been feeding all my goldfish pellets from the beginning (Of course combined with vegetables and live foods), and when I tried to give them some flakes that I have for my betta, they seemed to really struggle trying to catch and eat them.

If you're worried about the pellets sinking, you should rather get floating pellets and soak them for a few minutes before feeding I have a couple of really good brands that you may want to try out!!
JBL Novo Pearl, floating, meadium-sized pellets that soften quickly after only a few minutes of soaking
Hikari Staple Goldfish, floating, mini pellets that don't ever sink, but use to soften up in water. If you want to soak them, you'll have to do that for at least an hour or something D8 (Tried and failed...) However, these pellets are really dense, so it won't be a problem for the goldfish to eat them. Hikari Goldfish Gold is another type of the same pellet, only with color enhancing qualities.
Sera Goldy Royal, slowly sinking small pellet, really nice for the goldfish to eat since it contains extra nutrients so they'll grow better.

Generally about the sinking food, feed it slow, so your goldfish will see it and be able to catch most of it before it hits the substrate But every goldfish loves digging in the gravel anyway, so they shouldn't have any problems finding the leftovers Try not to give them too much either, that would pollute the water even more and more food would sink to the bottom.

Hope this helps!

So, I took your advice and decided to just see how my fish would do if I gave them a few of the pellets.  These arent the sinking kind though..or maybe they are, i'm not sure, but the black moor (I really need to name my fish lol) chased them around for a few minutes before actually getting one in his mouth, then, once he got one, it almost look like it got stuck.  My fish are pretty young and still pretty small...so, I freaked out when i saw it get stuck and decided to try pellets when they grow a little bigger
I'm quickly learning how much fun this hobby can be but also, how much work it is to do it right.  I am really thankful I found this forum so I can talk to other goldie lovers like myself

great advice, I will go get brine shrimp and will add peas to their diet. thank you!

If the pellets seem to be a bit large, you can always chop them in half with scissors after pre-soaking them. Smaller fish can chew them better. Peas are great to feed at least once a week to help their digestion and avoid swim bladder disorder.