A train without an engine cannot leave the depot . In the depot it can be sold - maybe you should provide a screenshot .

Thank for your reply.

Yes I agree.
But I did it :-)
The railjet train is without a locomotive and on the route. He's still in the depot, but he can't. And I can't even delete him.
I tried to do it again on a new map. Managed to.
Print screen: print-screen[e-mhd.com]
The map is also attached: https://e-mhd.com/transport-fever/rj.sav

you need add-on:

• https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=799823150
  
• https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1298083670
  
• https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=840539897

Can you delete the depot ?

I tried.
There is a train in the depot - it cannot be deleted. :-(

OK then click on the depot , it should take you to a list of trains in the depot and you can sell it but from the screenshot I think the train is not 'in the depot' but on the track at the depot so you can delete the depot in this instance.

Thank you for trying.
But, the train is on its way to the depot. Because:
First, the train was marked (without a locomotive) for the new line in the depot.
But the train couldn't get out of the depot because it didn't have a locomotive. The train is marked Line 1.
Then I go to sell the train. The train is marked: heading to the depot. But he can't move - he doesn't have a locomotive.

It's a cycle. Yes out and not in.

Maybe it would help:
Is there any mod that I click on the train and it disappears?

Sorry, for my simply english :-)

Yes it is a bit of a bug . Normally wagons cannot go anywhere without a loco but the control cars here are treated as locos not wagons by the game but have no power , therefore the train can go on the line but never move .

The control cars could have power added to them temporarily or you need to start the game again .

Apologies for this .

Thank you for your interest and help. Good luck!