When using remote play with my mobile data plan and not a wifi network, the image is sent...

I see, in order to isolate a bit more the issue. Can you try connecting the console to a completely different wifi network?
For example sharing mobile data via wifi hotspot and connect the console in that way.

Then connect another phone to your home network (or use the phone mobile data) and see how it goes with remote playing

Yes. If I’m on my mobile network at work and try to remote play I get black screen.

When I’m home on my wifi it works fine.

But when I’m away or even at home and try to remote play on my mobile network I get the black screen. Was working fine before. Don’t know what happened

Hi Terry. My name is Kyle and I'm an independent advisor.

An internet connection is required to enable and use Remote Play, but the remote stream will only go through your local network. Other data such as authentication has to be sent through Microsoft servers when using Remote Play.

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.

I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today despite this FreeKlipz

Depending on the network remote play can work or not.

I mean, if your current wifi network has some internal restrictions this can be the reason. Some public or private networks are managed by their respective IT department.

If you try using directly your phone mobile data remote play works as expected or not at all?

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today despite this Nimish

Can someone else double check for you if the Xbox remote play feature is working properly using a device in your house?
Also, are you trying to start the remote play session using mobile data or a public wifi network?
Or with both types of connections the error persists?