I’m trying to download the SAP GUI on my Mac to practice and learn ABAP. But the download page redirects to something weird. Speaking of which, is it really hard to get help/resources for something less mainstream and highly specialized like ABAP as opposed to a language like Java, C#.

Yes. Documentation will usually be behind a paywall as part of the consultant partner strategy. Developers pay to be trained and certified, as do customers, and SAP makes money on every transaction they service. It's the same for pretty much any closed source COTS product. Having a public facing community would lower their profits.

It's a shitty model from the dark ages.

I always thought you need a license to use SAP applications. I guess there may be trial versions but personally I've never tried. If you can't get access to an actual system video tutorials in youtube can be helpful. I won't really suggest learning ABAP on your own. Simple custom reports are easier but there just too many objects and terminologies that's specific to the SAP environment that a developer can be lost. There usually is a Functional consultant or Solution Architect that does the design and integration of the components. If you really want to get some ABAP experience, I suggest getting hired by a company which can give you the training materials you need to study it. On a side note if you want to learn ABAP because you found a side gig, let me know. I'm trying to find one. :D