Depending on your interests, that could be anything from: Fortnite, Tasker[0], NewPipe, Ublock Origin[1], Syncthing, xCloud and GeForce Now (until pretty recently[2]), RetroArch, the Dolphin emulator (as of iOS 14.4), and the most recent addition, NSFW Discord servers.
> android is just handicapped because I can't run a different OS, or screw around in the OS and change things to my whims
You totally can. I've been running LineageOS for a while, it's great. Improves my battery life, allows me to quarantine apps, gives me more access to the firewall for adblocking, and lets me get rid of cruft like the launcher. You can even completely de-Google Android, or install a community-maintained shim called MicroG that enables some of the features without the tracking.
The Android situation could be much better, this is why some people are excited about Linux phones. But I don't know a ton of Android users who are clambering to make it harder to use storefronts like F-Droid. I literally can not imagine going to a phone platform that didn't support NewPipe, I watch too many videos on my device, using the official Youtube apps would degrade the experience way too much.
I do think that the number of Android-exclusive things you can do is much lower than it used to be. It used to be pretty easy to make a compelling case that if you cared about flexibility at all, you bought an Android phone. I don't think that's the case anymore. But Apple still hasn't really stopped being Apple, so while the differences have become a lot less glaring, they also haven't completely disappeared. And sure, you can get some of this functionality back by jailbreaking, but in comparison the vast majority of the stuff you do on Android won't require root access, and all of the apps I listed above can be installed on a stock Android device without flashing or breaking anything at all.
Whether or not iOS users actually care about that stuff... :shrug: I suspect many of them don't. I'm not going to try and make a giant case about whether your average person on the street wants to be able to emulate Gamecube games on their phone. But I also don't really care; I'm a consumer and I want to be able to emulate Gamecube games on my phone. I'm a consumer, and I want to be able to install alternative Youtube front-ends that increase my privacy. I want to be able to block ads in my browser.
At the moment, Android provides an alternative for me. I'm very lucky that I never got locked into Apple's ecosystem so I don't have to make a choice between losing access to my credit card and being able to have a user-respecting Youtube client. But if you are locked into Apple's ecosystem, making a switch between phone platforms can be really prohibitively expensive and time consuming, so I sympathize with people who are in that position.
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[0]: To be fair IFTT is pretty good, but it just can't offer the same level of functionality.
[1]: I know someone will jump in on this, but adblocking in Safari is just not comparable to Firefox. There is no way to get what I would consider to be adequate adblocking on the web in iOS.
[2]: Microsoft/Nvidia have only been able to launch on iOS using webapps, which given Safari's current limitations are arguably a worse experience than having native apps.