Below you can find the direct links to download Apple's HomePod firmware files.
Latest:
14.4 (HomePod): AudioAccessory5,1_14.4_18K802_Restore.ipsw
Full List:
14.2 (HomePod): AudioAccessory5,1_14.2_18K60_Restore.ipsw
14.2.1 (HomePod): AudioAccessory5,1_14.2.1_18K75_Restore.ipsw
14.3 (HomePod): AudioAccessory5,1_14.3_18K563_Restore.ipsw
14.4 (HomePod): AudioAccessory5,1_14.4_18K802_Restore.ipsw
