Quorn and other meat substitutes most certainly fit the criteria of ultra-processed foods, and as such may be implicated in poor health outcomes if they make up a significant portion of one's diet.
> Among generally healthy adults, contrasting Plant with Animal intake, while keeping all other dietary components similar, the Plant products improved several cardiovascular disease risk factors, including TMAO; there were no adverse effects on risk factors from the Plant products.
The SWAP-MEAT trial concluded that processed alt-meat products improved health markers over animal meat: https://pubmed.ncbi.nlm.nih.gov/32780794/
> Among generally healthy adults, contrasting Plant with Animal intake, while keeping all other dietary components similar, the Plant products improved several cardiovascular disease risk factors, including TMAO; there were no adverse effects on risk factors from the Plant products.