I bought another BT adapter which was recommended by some redditors and on other forums online. It's called the Zexmte.
https://www.amazon.de/-/en/Bluetooth-Receiver-Transfer-Wireless-Keyboard/dp/B0775YF36R/ref=sr_1_4?crid=1O9HDOR0A0VYL&keywords=zexmte&qid=1642779605&s=computers&sprefix=zexmte%2Ccomputers%2C61&sr=1-4
In Mario Kart I now can reconnect 3 wiimotes, at least sometimes, so I guess it works better than the Ugreen adapter. Sadly however, The fourth wiimote won't reconnect.
In Mario Kart there is a workaround. You can go to the 4-Player Multiplayer screen and then add a wiimote by pressing + on one of the connected wiimotes. By pressing 1 and 2 on the missing wiimote, it will eventually connect. However, not all games have this function.
https://www.amazon.de/-/en/Bluetooth-Receiver-Transfer-Wireless-Keyboard/dp/B0775YF36R/ref=sr_1_4?crid=1O9HDOR0A0VYL&keywords=zexmte&qid=1642779605&s=computers&sprefix=zexmte%2Ccomputers%2C61&sr=1-4
In Mario Kart I now can reconnect 3 wiimotes, at least sometimes, so I guess it works better than the Ugreen adapter. Sadly however, The fourth wiimote won't reconnect.
In Mario Kart there is a workaround. You can go to the 4-Player Multiplayer screen and then add a wiimote by pressing + on one of the connected wiimotes. By pressing 1 and 2 on the missing wiimote, it will eventually connect. However, not all games have this function.