Limitations of the new Arduino Applab

I understand what you mean; however, for me it’s not possible to use the WebUI block because I cannot use CSS, Java, or HTML5, whereas the WebUI block relies on these elements.
As for “Arduino OS,” the Arduino Uno Q is an SBC — in other words, a computer — and the operating system of the Arduino Uno Q is Arduino OS, based on the Debian Linux distribution.

(If you want to use this mode, you need to connect a dongle that includes an HDMI port, at least two USB ports, and a USB‑C port. Then connect a power supply via USB‑C, a mouse, a keyboard, and a screen, and the system will boot. However, it is not recommended to use an Apple dongle, as it works poorly with the Uno Q.)