Unable to repurpose AirPort Express with EERO and Verizon router

After many hours still can't get it to work after hours with ISP and EERO.

I have a 2019 iMac and EERO working.

I have turned off wifi on Verizon router.

My connections are as follows:

EERO to VZ router, EERO to WAN of the Airport Extreme,LAN of Extreme to iMac

Using Airport Utility 6.3.9

In Airport Utility I have Wireless > Network mode OFF and Network >Router mode off (bridge mode)

Under other wifi devices I see the 2 expresses I have, yet cannot hook up to them per this support page

AirPort Express: How to join an existing Wi-Fi network in client mode - Apple Support

I cannot choose the repurposing option as it is greyed out.

I thought EERO was supposed to work with Extreme and Express?

Apple won't discuss as Extreme and Express are obsolete.

Has worked perfectly for years, but need a more robust wifi network, so I got EERO thinking it would solve my WiFi issues and let me continue to have the Extreme and Expresses work.

Likely, I have missed some specifics, happy to answer whatever i missed

Many thanks for assistance.

Running Sequoia 15.5

[Re-Titled by Moderator]

Original Title: AIRPORT AND EERO