Wireless Mouse Driver.

I’ve had this kind of keyboard with touchpad thing which has a dongle adapter. The keyboard part works well but the cursor jitters. Mouse buttons do work.
EDIT: The os was RiscOS 5.24 PI

Not all wireless mouse/keyboard devices work with all versions of RISC OS on all platforms. For example a recent Logitech wireless mouse, which has a dongle that can combine signals from a mouse and a keyboard, completely freezes RO4.02 on a RISCPC. It works fine on an Iyonix with RO5.18 and an ARMX6 with 5.25. An older logitech mouse dongle works fine with all of them.

Some devices show the weird effect of inserting key presses when the mouse moves.

Some of them work fine when plugged in directly, but not when via some KVM switches.

It’s a matter of luck, or trying before buying.

Krzystof, when posting, it always helps if you say the OS version / build date and platform (eg. Pi). For example, RISC OS 5.24/5.26 had some funny issues with keyboard/mouse that were resolved early last year (I think). Those fixes won’t be in “RISC OS pi” (5.24), but will be in “RISC OS Direct” (5.27) or the nightly builds, so it is helpful to know which version you’re running.

With dongle-based wireless keyboard/mouse sets, it can also be helopful (generally – this applies to PCs too) to try repositioning the dongle using a USB extension cable. It is not uncommon to see interference, or distance issues depending on other devices and spurious signals etc. For example, I remember installing a PC in a small alcove in a retirement flat for someone. It seemed very “normal”, and the keyboard/mouse were within two feet of the receiver. However, the connection was very jittery. Fortunately, his old wireless mouse came with an extenion cable which acted as a charger, so I used that to extend the receiver dongle to just behind his monitor. Bingo – all the jittering vanished, and everything was fine.

I had such experiencectoo, and found out: it is even worse on a RaspberryPi4 ( same dongle).
On the pi4, the problem even was present on Raspbian. Reason: Bluetoth interferences.
Check, if W-Lan/Bluetooth is off?

W-lan and Bluetooth is off, due to the unavailability of the wifi/bluetooth driver. But unlike your case, mine worked fine on any Linux.

W-lan and Bluetooth is off

I don’t think that is true, RISC OS doesn’t do anything with them, so they are in an undefined state, to turn them ‘off’ properly you would need a driver!