Trying to connect 2013 MacBook display to 2017 iMac screen. I have the cables, but no luck

Yup, it won't work. Please read Target Display Mode, Target Display Mode died in 2014. You can try third party solutions though. Please remember Macs are computers they are not external displays for other devices, including other Macs.

I've been using Luna Display to connect a 2012 and 2020 iMacs. They are both on the same Ethernet network and I response time is great. Rkaufmann87's response is spot on. I would recommend getting an external display.

Hope this helps.

Paul

I cannot recommend any, however I know Luna display is supposed to do it. Personally, I would simply buy an external display and use that, why you ask....simple:

1. Dead reliable.
2. Less expensive than expensive hardware/software solutions.
3. Simple to setup and use.

My iMac is getting very slow. Am buying a SSD, but would also like to keep using the screen with laptops if that doesn't improve things. Can you recommend the 3rd party solutions you mentioned?

Not all SSDs can be used as a startup disk for an iMac. What external SSD are you planning to use?

You're welcome and good luck.