You should never run any GUI application with sudo, not only on a “hacker distro”, whatever that means, but on any flavour of GNU/Linux. Never.
This is for several reasons, one of which is that it may mess up permissions of config files in your home directory, breaking other applications and creating strange errors which may manifest after many days, and are difficult to troubleshoot. But more importantly, GUI applications usually depend on many libraries, like widget kits, e.g .GTK or Qt, which in turn depend on dozens of other libraries, etc, etc… So, when you run even a simple GUI application with sudo, you’re running literally millions upon millions of lines of code as root, some of which were never designed to be run as root, and some never properly tested with root privileges. Obviously, this can cause all sorts of unpredictable, potentially system breaking side effects.
This is not specific to GUI applications, many terminal applications should also never be run with sudo. Elevating privileges with sudo should always be done with utmost care, only when it is necessary to do so, only with simple system utilities, and only when you know exactly what you’re doing.
So, when someone more knowledgeable than you tells you not to run thunar with sudo, it is wise to listen to that advice.
Also, EndeavourOS, just like Arch Linux upon which it is based, is a fully functioning system. Claiming otherwise just makes one sound silly.