Vado SL 4.0 with a suspension fork?

[Allan47.7339]

A normal steerer tube.

I don't think that is a precise enough answer if it referencing a Vado SL. The steerer tube is customized for the future shock system. As far as I know it's not a standard diameter.
Example is to delete the future shock, you need a custom part.

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[Stefan Mikes]

The steerer tube is customized for the future shock system

Not in Vado SL 1 4.0. Only in 5.0: it is a carbon fork. I use Redshift on my Vado SL 1 4.0; it's a normal steerer.