There are multiple types of squeak/squeal so it depends which one you have.
The one to do with the shim on shim or shim on pad contact I call a squeak.
It should be short squeak squeak squeak type sounds that will generally happen over bumps that allow the shims/pads to move a bit and squeak.
Brake grease is to go between the shim & shim or shim and pad.
Or as mentioned you can use disc brake quiet. I also use that and have no problems.
There is also the spring metal parts that hold your pads to the calipers. These can make squeak squeak squeak sounds over bumps also and should have a layer of copper grease to avoid such noises.
If you look at the workshop manuals here
viewtopic.php?f=12&t=4686#p185940It has diagrams of where to put grease.
The above noises should be related to movement from things like bumps and will generally happen at any speeds.
The sound I refer to as squeal is usually a longer squeal type noise instead of short sharp squeak squeak squeaks. This noise is from the brake pad on rotor contact and is related to the brake pad compound (and apparently incorrect bed in procedure can also be a factor). That's why you see on brake pad brochures information about noise. Often high performance brakes can be a bit noisy.
This noise should only happen when you are braking and has nothing to do with bumps.
It usually only happens when you are very lightly applying your brakes, usually at low speed, like when you are stuck in traffic and creeping forwards, or coming to a stop at traffic lights.
It is much less likely at high speeds and you shouldn't get it under normal and hard brake pressure (unless your pads are worn out or you have something stuck between your disc and pads like dirt or rocks).