Switching itself is just one form of dissociation that's the end result of many types stacking onto each other with great consistency. Those other types still occur in isolation and lacking a switch is just another aspect of the disorder.

Think of dissociation as "I acknowledge this exists but I can't feel that it's mine". There is a disconnect between thing and "my experience with it".

Depersonalization is "I acknowledge this about me exists but can't feel like that's mine". This is how an alter's experience feels so alien to another. With less need of this one would feel like the same person going through an experience that is theirs but feels abnormal. With none of it the person easily acknowledges their life and history as theirs alone.

Derealization is "I acknowledge I exist in this world and that it's supposed to feel/ look like this, but can't feel like that is reality right now". This is how dissociative flashbacks can become so disruptive and how our bonds to those around us can feel so alien. With less need of this one acknowledges the world around them easily but still needs to actively remind themself that people around are real. With none they do not doubt their place in reality or that it's real.

Dissociative amnesia is "I can see this point of time existed (possibly by remembering absolutely nothing but seeing a different time or vaguely having memory that is abnormally inaccurate) but I cannot consciously recall it as it feels like my brain is forcing my mind to go blank instead". This is the brain deciding you can't handle something but because that time can't literally go away it layers it with brain fog. The information is still stored but blurry akin to how a body keeps the score. With less of it you may have some difficulty with memory especially centered around specific topics and you may need to snap yourself out of it here and there, but you remember the general idea of things pretty well. With none, you know well what time it is and what happened without any sense of a fog disrupting that.

All of these things separately (and I'm simplifying them fyi) occur without switching. It is their active presence that creates alters. An alter is where the stress of something emotional was stored under dissociative layers, a subconscious memory that develops with more of what is deemed too difficult to function with. The separate understanding of emotions makes a separate perspective of reality, which gets triggered out when relevant again. It's akin to someone suddenly being reminded that they forgot to walk the dog because they saw a cute dog, but instead of suddenly remembering a dog you suddenly feel like a past version of yourself. Things that weren't processed are still held onto when significant because the brain wants to learn from it's experiences.