Airplay 2
I can't play 2 different speakers/rooms at the same time on my Iphone 8. It is possible from my macbook when I use Itunes.
One of the speakers is connected with airport express.
iPhone 8, iOS 13
Hmm, your 1st gen AirPort Express model came out in 2008 and were discontinued in 2012 ... so it can be a bit "long in the tooth." Regardless, I found here at the ASC, a number of folks (including myself) finding firmware v7.8.1 to be problematic ... especially with streaming from a Mac running macOS Catalina or iOS devices running iOS 13+.
As you are probably aware, Apple exited the AirPort base station line about 2 years ago. I was actually surprised when they released v7.8 & 7.8.1 after stopping production to (supposedly) provide AirPlay 2 support for these base stations. In my testing of both 1st & 2nd gen 802.11n Express base station, I found inconsistent results with streaming from both macOS & iOS devices. The only "solution" was to downgrade their firmware to 6.8 or 6.9. Of course, that disabled AirPlay 2, but it still allowed for streaming.
One other thing to check. AirPlay requires IPv6 in order to discover an AirPlay "speaker." As a minimum, your network (wired and wireless) should be configured for IPv6 Link-local only. Is it?