There is no semi transparency in GIF.
You can see possible examples that i attached below. They don't work on posts but you can observe them with opening images in new tabs.
You can upload PNGs frame by frame on https://ezgif.com/webp-maker and try to make transparent animated images.
or
You can export> render video> quicktime (straight unmatted) in photoshop and convert your mov to webp on https://www.onlineconverter.com/video-to-webp
After these, we need a frontend developer. Because I don't know that can webp format play in posts? or is there a embeded code that plays webp? I hope I could help you.
Or
You must make a really good pixel work on GIF =)
They are also not pixel perfect on light mode too.😊
Ohhhhhhhh looks like a lot of work, lot of technical stuff but i will try some to see:)Thank you much for the advice @bidesign, really valuable:)