Which preview setting did you use?

I'm on "Preview - Auto", but that's not the problem, even after a proper render the text is still blurry...

Any chance to share a sample Vegas Pro project file including the text pic?

Here you go : https://www.dropbox.com/s/anvm0z0ao8fvpsm/Crawling_text_002.veg?dl=0

And here is a test render :  (you can see the text is blurry, like a low resolution pic)

Mmh, not sure about it. To me it looks like the blur you'd get from scaling (it looks sharp in the foreground). Unfortunately your download doesn't contain the pic so I could not repro or compare to the original source.

Maybe your project properties/render settings could have been optimized by selecting "best" as render setting.

Oh sorry, I thought you could obtain the pic from the Vegas file. Here it is : https://www.dropbox.com/s/60dxsalr00ek1rp/Crawling_text_episode1_transp_big.png?dl=0

And changing the render settings to "Best" isn't changing anything in the final render...

I think it's due to downscaling the 8177 x 4600 to HD resolution in a first step (the project properties) and further scaling done by TrackMotion.

If you apply a sharpen filter like Unsharp Mask you'd maybe better apply as track fx instead of event fx because the blur introduced by TrackMotion is ignored otherway.

Also if you generate text inside Vegas Pro using one of the text generators you maybe could avoid further scaling.

Oh ok...

I tried to apply the Unsharp Mask filter to the track, but it didn't do anything great...

And I tried doing that using a text generator in Vegas but, as the text goes away, the upper lines are disappearing, because they just leave the 1920x1080 frame, that's why I did this big text pic.

Using the Vegas text generator you can adjust where it cuts at the top and the bottom by i.e. adjusting the Y position (at top and bottom in the Perspective) when you have set the lying angle by adjusting the X setting in Orientation...

I can't quite do that because the frame in a generated text will always be at my project size (1920x1080). But the text itself can't fit in a 1920x1080 frame, it needs much more space to be readable. That's why I created this 8177x4600 picture with the text in it, so I can afterwards move the image through the screen without any text being cut.

I don't know if I'm clear, or if I don't get what you're trying to say, english is not my native language...

Make your canvass for the text higher but not so wide. That way your text can be larger and your canvas smaller. In most photo programs you can make whatever resolution you want so make your text to all the way side to side and make it as high as it needs to be.

Yeah I already did that, but the result is exactly the same, because the height of the canvas stays the same.

But you still get rid of all of the unneeded data. Okay, when I use the 3d settings at about the same angle has you have, it appears softer to me as well. May just be the way the file has to be handled.

This was created using After Effects, besides some compression artifiacts and youtube's treatment, I think it looks sharper

In Vegas Pro if you use a 4k project it will be much sharper, too, because the base feeded to TrackMotion is of higher resolution.