First of all, this is awesome!
Possibly the best platformer I have played on C64.
Second:
I found a bug.
If I spam down and up really fast, I can perform multiple jumps mid-air.
https://static.juiffi.eu/spelunky4_infinite_jump.mp4
x64sc.exe
3.8
(GTK3 3.24.39, GLib 2.78.3, Cairo 1.18.0, Pango 1.50.14)