I've had a bit more time to play this... fiendishly challenging but absolutely brilliant!
A couple of bugs to report in the Linux version via the itch app:
1) There are no trees rendering on the top of the waterfall hill unlike in the speedrun. Did these get removed?
2) On the volcano island the trees are not clipping (cat can go straight through)
The Linux zip is somewhat larger than the Windows and Mac zip, so it is just an older version?
Also some suggestions:
a) Pressing jump again while in the air on the capybara should cause the cat to jump off (dismount mid-air). That just feels natural. Once the cat is off the capybara and in the air, pressing jump again does nothing.
b) More music variants of the Stock Market music theme on the main map (if you've ever played Banjo Kazooie on the N64, the way the same melody morphs between instruments as you move between areas is just magical!)
c) Add the ability to climb into the trolley whenever the cat is on the capybara. Just before the cat climbs in he should give the trolley a little push. There should be no way to make the trolley move forwards once in it, so it'll carry on rolling any distance if on a hill. If in the trolley, you can't throw the trolley obviously and rockets are disabled.
d) When the cat is off the capybara, If the player manually jumps onto the capybara (as opposed to pressing the mount button), this should also cause the cat to mount the capybara again. Feels natural.