How long ago? My group of friends switched to Signal a few weeks back and there have been no issues with push notifications for me on iOS. It might be worth another look if it's been a while.
Only a couple of months ago (second time I tried, both times same issue). This was on Android btw. To be clear I meant the push notification on my own device didn't work (reading back I can see what I said could be misinterpreted). I suspect it had something to do with aggressive background process management but even switching everything to low power efficiency settings/ always on didn't work consistently. I've moved on.