After reading your post I gave another look to the theme file, which had GSAP 3.6.1 and ScrollTrigger 3.8.0 a couple thousand lines below (this one was actually the culprit of the errors, and I didn't see it before). Changed the code from both with the versions 3.11.3, queued the ScrollSmoother 3.11.3, and so far console is clear of errors, with a smooth scroll.
Now, like @Yannis Yannakopoulos said above, I will run into problems with a theme update, but for now it seems to be all good.
