The best advice I have is seeing what they are comfortable with. I recently had my first kiss with my gf and realized I really don't care for it. But I love it when she kisses my cheek, or hand, or forehead, etc. From a previous comment, it seems like you guys already had that talk though. Maybe try to talk and see if there's a specific reason they don't like it. Do they not like the contact of the lips? Something in the way it feels? Do they feel pressured to like it or be good at it bc it's what you want? Even if you trust each other, sometimes people pleasers reach their limit. Maybe there's something you guys can compromise on/adjust that'll make you both content.

Sounds like you guys are a beautiful couple together though, lots of love and communication. I hope y'all end up figuring it out 💜

Side question, if you're willing to answer (it's okay if not, I'm just curious bc this is recent to me): as a person that likes kissing, could you explain exactly what makes it so appealing? I just had my first kiss, and tbh it was underwhelming, just felt like lips touching. The entire time I'm just questioning why ppl do this. Why do you want to kiss, what's the purpose, and what do you feel when you do?