how to connect iMac 2017 and iMac 2023 screens?

Not possible. Only a few older models were ever capable of "Target Display Mode." No 2017 or 2023 iMac is capable of doing it.

OTOH, screen sharing may or may not help you do what you want. (I don't think it will, but it's worth a look. I believe screen sharing is essentially 'mirroring' via network, which would mean that both screens would show the exact same images, it would not be an extended desktop.)

I haven't tried it, but Turn any Mac or iPad into a second display...

https://lunadisplay.com/

https://www.duetdisplay.com/

Duet - Remote Desktop, Second Display, Drawing Tablet, and More (duetdisplay.com)

Review by NAK005, you may not be happy with it…

Secondary Screen Solution - Apple Community

Hmmm...

1. On your Mac, choose Apple menu  > System Settings, then click Network  in the sidebar. (You may need to scroll down.)
2. Click the Action pop-up menu  on the right, then choose Set Service Order.
3. Drag services into the order you want.
4. Click OK.

Hmmm...

1. On your Mac, choose Apple menu  > System Settings, then click Network  in the sidebar. (You may need to scroll down.)
2. Click the Action pop-up menu  on the right, then choose Set Service Order.
3. Drag services into the order you want.
4. Click OK.

Does that affect it?