I had quite a few problems connecting some of the IKEA Matter devices.
How I succeeded:
I took my old Android phone, did factory reset, and only installed & configured network and Homey app.
Keeping phone, Homey and IKEA device really close (less than 50cm) and using Android connection.
It took a couple of tries but all the sudden it worked just fine!
My struggle described here:
Thread network question - Questions & Help - Homey Community Forum
