HomePod says I'm up to date

I had this problem too, restarting HomePod, from Home App., fixed this issue for me.

Update became available and now on version 14.5.

give it 10 - 15 mins after restart, before update becomes available. That's how long it took for me to see update, post restart

I also had this problem. Did the restart. Nothing. However, I then killed the Home app on my phone and restarted it, and the update came up. So maybe give that a try.