Session props would be your best bet
session.props.device.userAgent
though the userAgent has been somewhat muddled by browser makers
here’s what my Firefox looks like
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0
and here is my Chrome one
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36
further reading https://towardsdatascience.com/the-user-agent-that-crazy-string-underpinning-a-bunch-of-analytics-86507ef632f0