Answering "thank you" to "I love you" is a polite way to deal with unwanted advances of another person. The reaction emoji under the message is commonly interpreted as "thank you".
It's even more confusing: Emojis were invented in Japan, which adds another layer of cultural differences. Holding your hands flat against each other is a common sign for prayer in Christianity, but in Japan it is a commen gesture for giving thanks. Hence the "official" meaning: Thank you
Commonly high fives arr given by the palms of the same hand therefore the thumb would've been visible at least on one of the hands if ot was a high five emoji
🥺🙏 you can submit a high five emoji idea here, but I haven't checked if there is actually a high five emoji or whether or not it has already been submitted
https://www.unicode.org/emoji/proposals.html