MonkeyDev VS theos-jailed

I can't read a lot of that project, but what I can doesn't look like you'll be able to do that on an iPhone. If you look at the installation section, it's expecting you to be building this on a mac: https://github.com/AloneMonkey/MonkeyDev/wiki/Installation (that isn't called out explicitly, but it's implicit in the commands they're running). "Easy to install" in this case seems to be for someone who is familiar with writing custom iOS applications and has a development setup for that already.

Theos is the easiest way to do it imo but you can still use Xcode with something like MonkeyDev if you want to. Either way you'll need to install theos

There's tools that can do that for you. Theos-jailed (https://github.com/kabiroberai/theos-jailed), Sideloadly (https://sideloadly.io), and Azule (https://github.com/Al4ise/Azule) are probably the most user-friendly ways to do it.

I’d give Theos-Jailed a try. Seems like some people (at least in the past) got it to work.

Here you go: https://github.com/kabiroberai/theos-jailed

The 2 widely-used tools for bringing tweaks to jailed devices are kabiroberai's theos jailed and Brandon Plank's iPAPatcher. Both tools, though, have their own issues.

check out theos-jailed, that’s how tweaked IPAs are usually made.

It does! You can add dylib files from the Libraries section of the editor and supporting files to Resources (after which you may also need to hook the framework’s code to change where it looks for the support files). Following that, you may need to hook the dylib’s methods that fetch resources in order to point them to the right folder. Note that I also have a detailed explanation of how to do something similar in Theos Jailed’s docs: see https://github.com/kabiroberai/theos-jailed/wiki/Usage#injecting-a-cydia-tweak. Good luck :)