The HG freehub bodies must be MTB or road specific for a reason. You don’t need a spacer with an 11 speed cassette on a DT HG body.
OK…
11 speed road HG is a marginally longer interface standard than HG (of old). The length is gained by reducing the depth of the “bed”. The actual freehub is the same physical length and will not alter the width of your hub. It will however require a spacer to work with a 9 10 or mtb 11* speed cassette. Without a spacer the cassettes will be loose, with a spacer when it’s not needed, the lock ring won’t engage.
A boost wheel shouldn’t fit a non boost frame without some effort to flex the frame, 6mm is a lot. (iirc stanton and possibly a few others do a 145 dropout on their steel frames to accommodate both widths).
The 6mm width is fully accounted for left of the freehub, the freehub end is in the same place relative to the face of the end cap on non boost, boost and (I think) super boost wheels, there are no spacers etc to move the freehub in or out relative to the hub body. Even adapters** (correctly) space the wheel 6mm from the nds, meaning a redish and leaving the cassette in the same place
When you say the cassette is binding, do you mean it contacts the frame?
My guess if it physically goes into your (non boost) frame without forcing it is you have a 142mm wheel but you’ve measured at 148 🤔.
Try fitting it with no cassette on and see how it looks…
*some newer ones apparently fit road 11 without a spacer as that’s generally what everyone has made for a few years, I can’t say I’ve ever seen a mtb cassette like this mind but I’ve been on xd for years. (11 speed xt cassettes used to come with a spacer, there should only be one behind your cassette, the one which came with the freehub does the same job for cassettes supplied without).
**some adapters put 3mm either side so you don’t need to redish, instead you need to reindex and hope your mech has enough range to reach top (sram do not in my experience)