If you decide to use glyphosate beware of two things. Multiple applications will probably be needed and using products designated for agricultural use could land you in trouble. There's good reason why agricultural and retail glyphosate products are of different strengths.
Some reports suggest glyphosate is carcinogenic.
I used agri grade glycophosphate to clear an old abandoned graveyard of runaway brambles, before cutting back to create a wildflower meadow. The local council professionals advised glycophosohate and I took all precausions with PPE etc.
I disposed of the remaining gpp by giving it to the local nature conservancy charity.
Some agri workers used to get soaked in the stuff yearly, which is probably not good.