would you say shoujo boys are a Character Type in a distinct manner from the way shounen girls are?

oh, absolutely. while of course the overall character trends present in both genres can be very broad and leave room for a lot of variation, much like how the archetypal shonen girl is defined by her potential romantic relation to the protagonist, the archetypal shoujo boy is perhaps even more so. this is because while shonen absolutely includes romance as a component of its frequently-escapist storytelling, shoujo almost ALWAYS includes romance as a main focus.

(disclaimer that I'm talking very very broadly with trends I've seen in the genres, and not about specific individual works. there's a lot of shoujo with mainstream popularity that deals with telling different types of stories, and the same is true for shonen. it's just also true that it's been very rare for me to encounter a shoujo work that isn't romantically focused, and I spend a LOT of time scrolling manga sites to find shoujo when I want to read something chill.)

for the shoujo boy, the specific archetypes he's drawing off of tend to be what's currently in fashion at the moment, but the common denominators tend to be that he is older, usually more "worldly" than the protagonist, and possesses great social, political, or magical power. if he's in a fantasy story, he is either a duke or a prince. if he's in a more modern story, he is likely considered to be at the top of a social hierarchy. you'll notice that all these factors translate to him being more powerful than the protagonist. this is for a very specific reason! a critical component of shoujo romance stories is that the hero almost always needs to be capable of protecting the heroine in some way.

you could make an ENTIRE gender studies course on this, but I won't digress into that very interesting tangent. here, I'm just attempting to identify the common archetype and the fantasy underpinning that archetype. for now, it's enough to say that the fantasy of having a boyfriend who can protect you is nearly universally shown in shoujo romances. these tropes are usually true of both main male leads and any secondary love interest that the protagonist picks up, btw.

another critical component of the archetype is that the shoujo boy has a wound that only the female protagonist can heal. whether that's physical (guy undergoing a magical transformation into something, guy with rare magical disease, etc) or emotional (usually the guy's got some trauma,) there is almost always something uniquely healing about the protagonist that draws him to her. if he's a womanizer, she can make him faithful to only her. if he's brooding, she possesses the ability to make him smile. he is always thinking about her. it's difficult for him to take his eyes off her when they're in a room together. and if he isn't someone who is usually gentle to others, somehow he is capable of being gentle to the protagonist.

honestly, i would say his actual personality is way less important than his story utility. whether he's a sweet childhood friend, an overbearing romantic pursuer, a brooding loner, or anything else, it's almost always true that a major male character will present some traits of an idealized male love interest as mentioned above. his personality traits outside of that will just appeal to varying and more specific types of fantasy boyfriend.

the shonen girl, by contrast, often requires a very specific personality type to be the object of desire (and usually the object of plot) in her story. while there are exceptions, the most common shonen girl archetype that I've seen is just kind of generically feminine and sweet. if she fights, she often loses. if she tries to be active, her attempts at agency will end with her being damselled. think kairi from kingdom hearts or orihime from bleach.

on that note, that's also a major point of divergence between the two archetypes. while the shonen girl frequently exists as a plot macguffin and object of desire, the shoujo boy is very frequently a driver of plot. whether he's swooping in to save the protagonist from an evil dragon, fighting the protagonist in an academic rivalry, or the protagonist's arranged-marriage husband with a big secret, he usually moves the plot forward with his actions. though the honor of main plot driver either goes to the protagonist herself or to outside forces such as a villain, every major male lead in a shoujo story will contribute to the plot momentum in some way. again, you could write a gender studies thesis on this.

but that's my broad analysis of trends! I'll note that the bulk of both shoujo AND shonen I've read are almost always fantasy, so my perspective of big trends might be a little skewed to those genres. I'm not too sure what usually goes on in shoujo with contemporary settings, for example. feel free to add on with any thoughts of your own, especially if you think I'm off base about something!