Maybe making "bread" which is almost entirely cellulose would be possible. Still a carbohydrate, but not a digestible one.

This is what most keto breads are. Source: the two loafs in my bread drawer that report 23g of carbs and 19g dietary fiber. Some of that 19g is cellulose.

And how’s the taste in those?

It varies by brand and type. Some are pretty bad. Aunt Millie's has a couple of really good ones, particularly their 5 seed and white. Aldi's white keto is good, too. Lewis has a good keto Hawaiian loaf. For whatever reason the keto wheat breads I've tried are a little too... woody for me. I'm not sure if they are available outside the Midwest. To be honest, I'm really happy keto bread exists because for about two years, I couldn't eat sandwiches (I have to eat less than 50g of non-fiber carbohydrate per day... so just the bread on a sandwich usually takes 90% + of that).

It usually is made of almond or coconut flour. Most "keto" bread isn't devoid of carbs, but often has a lot of dietary fiber, which is undigestable.

Almond and coconut flour are likely to have more (natural) sugar in than wheat flour. Bread made with coconut flour in particular is surely going to have more total sugar than regular bread with a little added sugar.

A more reasonable explanation is that the comment that triggered this discussion was just from someone who used the wrong word by accident or totally misunderstands what carbs are.

The gut doesn't absorb sugar as well in the presence of fibre so I think people tend to subtract the amount of fibre from the total carbs to come up with something called net-carbs. No idea how well this works in practice of course but there is definitely some high percentage of sugar not absorbed for every gram of fibre added.

I'd say at that point just give up on eating bread. Something bread-shaped and fluffy could be made of anything.

Sorry brain fart there!

Anyway now I have changed the subject here is an example

https://www.woolworths.com.au/shop/productdetails/164022