bear with me while i download a few different versions and then write something out...OK omg. you've already got a ton of great input from people who are WAY better at drawing dogs than i am, but i thought your art was so cute and fun that i kind of wanted to draw next to your drawings anyways!!!! and then i got carried away. im so sorry lol you're not obligated to read this
rather than tell you to look at reference, study dog anatomy, etc (because you've already received that advice) i wanted to come at it from a different angle. if you wanted to, you could play with cartoony proportions and stylizations. this is just one direction to go with art -- no idea if it's a direction you're interested in -- im just presenting it as an option.
your style is so fun, i really love the angular shapes and the soft curves combined, it's just really satisfying! which i think is what made me really excited to suggest you push it even further. you mentioned having trouble with characters looking the same -- i would encourage you to mess around and try out radically different proportions. make the face really short. or really long. push it up, a really upturned snout, or have it hang down with big jowls, like a st bernard. push it further than you think is reasonable. do the same with the eyes, with the ears, with the body -- make some truly wild creatures. you can always pull it back, but doing this kind of experimental, explorative drawing really helps add diversity to your art. try new things and most importantly just have
fun and let yourself play
i don't have aphantasia, but i do struggle with my minds eye. im really not good at picturing things clearly, i think that's part of why i was drawn to art honestly, because im searching for that thing i can't quite see. i need to lay it out in front of me to know it.
tangent aside, i also rely heavily on muscle memory when i draw. branching out and experimenting, discovering what can come out of your hands when you're bold enough to make marks you've never made before, is the only way i really know how to break past that repetitiveness you mentioned. art is a tactile medium, i think there's no shame in approaching it in such a tactile way -- learning through making the marks and seeing what they become.
it's very important to have an understanding of what you're trying to draw -- anatomical knowledge and a 3d understanding of it for instance -- but it's also totally fair game to then stylize it to all heck. the more you understand about the subject, the more intentional and nuanced your stylization of it can become. but im not gonna sit here and lecture you that you need to "know the rules before you break them" or anything. art is what you make it. it is anything you want it to be. you don't have to deny yourself fun and whimsy and the ability to just draw whatever you like, however you like, until youve "mastered the fundamentals" or whatever. it's so rewarding to study and improve your art, but never let studying ruin the fun and joy you get out of drawing. (honestly, i think this is more directed at myself than at you...) all that to say, feel free to find shorthand and stick to it -- if you construct your drawings out of the same few kinds of lines over and over again, i would just call that efficient! learning how to modify those muscle memory patterns to achieve different effects is where it really starts working well, i think
okay, ENOUGH with the tirade... no one asked for a novel, but i could just talk about art forever!
heres a few extra notes that i drew, im sorry these drawings are REALLY rough haha... my excuse is how late it is rn, i need to sleep. hopefully you're able to get something out of them anyways?
(another quick note -- i focused on the face, but pretty much everything im saying can be applied to the body as well. the body can be understood with basic geometric shapes, can be abstracted into lines, can be experimented with proportionally etc)

this is just one method ive learned, not the only method out there. please take this with a huge grain of salt... i am pretty sure this is NOTHING like actual dog anatomy... this has more to do with cartooning. i guess my personal approach is, if you're anthropomorphizing the character to have human thought and emotion, you may as well give em a human-like face to emote with lol

this is really just my personal approach to drawing faces -- everyone has a different art process, i just thought id demonstrate mine. i just throw down the circle as a guide and then start at the like, bridge of the nose or cheekbone? and just follow that line around all the way until it reaches the jaw on the other side. it takes 4 seconds or less and you can get so creative with modifying it, i didn't give you very good examples though unfortunately lol today was not my best drawing day

this is that muscle memory thing -- there's just shapes my hand is familiar with that i repeat all the time. i feel like everyone has something like this? it's like a fingerprint, you can tell someone's art by the marks they make. you don't have to craft it intentionally if you don't want to, but i would encourage experimentation with marks just to find new things you like i guess. in terms of what i meant by easily modifiable -- i mean mostly in proportion i suppose, the same fundamental structure, but make it shorter, wider, more curved, sharper, bigger, smaller -- anything. such simple shapes and lines are really easy to iterate on just by making one section longer or shorter, changing the relationship of the angles, making the parts closer together or further away from eachother... ok okay im shutting up, im shutting up now for real this time lol. i hope you were able to get anything out of this !!! your drawings are epic, i love your style, keep up the great work you're doing awesome !! π