@kl3m3n On another, unrelated topic- I use the ESP32 arduino core version 2.0.3-RC1, since it adds support for the newer ESP32C2, C3 etc. This version works fine with the BasicBluetooth demo you provide, and I am using straight Bluetooth for my current project.
However, out of curiosity, I tried to compile the GUI-O_BasicBLE demo. It wouldn't compile. It turns out that I had to remove the existing,older ESP32_BLE_Arduino-master folder from my Library folder. After that ,it will link with the proper BLE library that comes with the ESP32 vers. 2.0.3-RC1 core. Other GUI-O users, who have also upgraded to the latest ESP32 core library, may have the same issue if they have that other, older library installed.
BR