To piggyback on mooreds - you need a baseline to see what your target market uses (if you’re making the business decisions)
An easy answer is to add Google Analytics to your site and support browsers that account for greater than 0.5% of your visitors
Depends on the situation. I worked on a site for lawyers and we needed to make it work in IE11, because that was the site all the lawyers used.
I was just at a bank the other day and saw IE being used. It is still 8% of the wider market: https://www.netmarketshare.com/browser-market-share.aspx?opt...