Impossible to connect my light bulbs since I have a new routeur

Hello I contact you because I have two lightbulbd from yeelight. For months they worked without any problem. But one day I changed my router and it became impossible to connect them and to use the application. The errors I get when I try to connect them are “Device disconnected” or “timed out” and I’ve been trying for weeks to fix the problem. I have changed my DNS to etc, restarted my box, deactivated the 5ghz wifi, I don’t know what to do anymore I find it unacceptable.

best regards.