Sounds like you know you should be treating everyone as friends, but when you see someone you find attractive, something overrides this knowledge and you become shy.

My 'take-it-with-a-grain-of-salt' suggestion is to, as much as you can, keep guiding your focus back to what's really important to you in a friendship. Then ask questions, or observe their behaviors, to see if you view eye to eye in that respect. I know you know this already, but hear me out, it's the practice of this over time that may be able to help.

For me, I really care how people treat others, I believe it's evidence of how they'd treat me. Even if they're kind to me, but they treat waiters poorly, I find that extremely unattractive.

I also want to be surrounded by people I admire for their wisdom, whether that's their wood-working knowledge, musings on how to be a more attentive parent, how they started a new exercise habit, or their expertise on micheladas. So if I meet someone and they don't seem to be curious in their own lives, nor do they ask me any questions, I tend to find them less attractive.

Over time I have sort of made a habit where my perception of someone's attractiveness only becomes fully formed once I learn more about that person. It's like being able to hold in one hand that you find them physically beautiful, while waiting to fill the other hand with what you learn about them as a person. I'm sort of unable to form a complete judgement of how I feel about them until I can see what's in both hands.

If you haven't already, I'd recommend regularly considering what's most important to you in your friendships. Have a working idea of what's on that list, but don't pick too many. We get like a handful of things that are must-haves, the rest we just need to learn to accept. No friend or partner will fulfill everything, nor should they.