This isn't necessarily an easy question to answer, due to the complexity around determining what is / isn't novel.
There are some examples in Regulation 2018/1023 that might fall into the group you're thinking about - for example sugar cane fibre, or phosphated maize starch used for it's relatively high (>70%) fibre content.
The "novel" status may relate to the process to which the material has been subjected, rather than simply the source from which it is derived - obviously both sugar cane and maize have an extensive history of consumption, but processing them in ways that changes the nutrient balance and/or chemical composition potentially renders them novel.
There is a defined process to check whether something is or isn't novel, via your member states' competent authority. Although it sounds like you're looking at using ingredients in finished products, in which case it would be a question to put to your raw material suppliers.
There is also an online novel food catalogue operated by the Commission: https://webgate.ec.e...food_catalogue/
Understandably this isn't exhaustive, as it would be impossible to catalogue everything, so it's most useful probably as an initial quick reference point.
If the products are novel, they need to go through the formal assessment process defined in regulation - placing them on the market prior to this would not be legal. There is a bit of an overview of the processing on this EFSA page: https://www.efsa.eur...raditional-food
Assuming the products aren't novel, you can use them subject to meeting any other regulatory obligations that apply for the product. As mentioned in post #2 this would include contaminants limits, along with pesticide residue limits etc.
Additionally if the source of fibre is also considered to potentially be an additive then there may be maximum usage limits and/or category restrictions. The only potential fibre source I can think of that would fall into this category is polydextrose (E1200), which probably is outside the scope of the vegetable-based ones you're considering, and in any case IIRC it also has a quantum satis limit in most categories, so isn't really restricted in that sense anyway.