Well it is illegal but it depends on where you work. Some smaller companies never ask for an EAD again. I worked at a small company and they never asked me for my EAD again even after it had expired. I had gotten it renewed but they never asked for it so I didn’t mention it or anything. If they would have asked about it, I had the new one already so I just left it at that.
If you want to read up further:
https://www.immi-usa.com/uscis-unauthorized-employment/