You can absolutely write to ThingSpeak with an Uno R4 wifi. You can use any wifi library (its probably built in) that lets you write HTTP commands or create and MQTT interface.
Im not 100% sure that the R4 will work with the existing version of the ThingSpeak Arduino library (I do not have an R4 wifi.) My brief look at the product shows that its based on an ESP32 sx chip, of which I do have similar devices and I am able to use directly to read and write on thingSpeak both with and without the library.
