Can you tell us how you did the outline? My rough guess is it might help applying modifiers if there are any.
Could you let us see the model on sketchfab to see what exactly is wrong? You can just set it private, publish it and share the link here afterwards
I try that but sadly nothing happens.
i use this method https://www.youtube.com/watch?v=D4T1cDJryOI
also here is the link to the model.
Looks like there are two overlapping meshes. That flickering occurs when Sketchfab can't decide which face to display, when two meshes are exactly in the same place. Can you check that there is not a duplicate of your mesh left once you applied all modifiers? Also try to "remove doubles" on all meshes just in case. Feel free to send the .blend over, I can take a look!
Agree with @elbriga, the mesh and it's solidified version have faces that overlap and depending on the renderer, it can lead to z-fight like this. You need to have an offset between the solidified parts and the original mesh to avoid having both rendering at the same time, and the first thing to check if the Solidify parameters can help to achieve this.
I personally don't know enough about it yet to give you a direct fix, maybe someone in the community already had this issue or the knowledges to help you ?
I keep you in touch If I find a solution on my side