So you might legally be somewhat limited in what you can write there (like "donate to me SO THAT I can write more code YOU enjoy"), but saying
"Support me / donate to me / Support my work through Ko-Fi"
is entirely fine.
I don't think it's a worthwhile risk to take for Finnish open source developers to accept donations and think it won't be considered illegal by the authorities.
Nothing makes me happier than seeing you guys having come so far since then and having stayed so determined!