Q.allelopathy in blackberries
Are blackberries with thorns (not certain of variety – Navaho?) allelopathic? Having trouble growing lettuce next to my small blackberry patch. I know it might be the retarding effect of a tangle of traveling vines underground, but the number of berry sprouts popping up is not THAT much, plus the tiny lettuces are shallow-rooted. Problem made me wonder if blackberry is allelopathic. Any suggestions?

No, there is no research that shows Blackberries causing growing issues to other plants.
Lettuce plants can be finicky about soil and prefer cool weather to grow.
Here are some links with more information.
https://www.gardeningknowhow.com/edible/vegetables/lettuce/growing-lettuce-containers.htm
https://www.gardeningknowhow.com/edible/vegetables/lettuce/growing-lettuce.htm