Roku remote flashing green light

It's possible the remote has failed. You can't use a basic IR remote, so you have to have one of the WiFi Direct remotes. I think the current voice remotes will work on your 3600, but consider this first. Your Roku Stick 3600 is now an eight year old model, regardless of when you actually acquired it. I have one but it's no longer in use. And it will most likely be in the next batch of older players that Roku will discontinue support for. And even if it remains supported for another couple of years, it's still old and nowhere near as powerful as any of the currently available players. Even the basic Express model, which is not 4k capable, is significantly improved over your model, and the Express 4K+ or the current Stick are even more capable, with support for 4K HDR (the Stick supports Dolby Vision); more memory, faster processor, and both come with a Voice Remote (that yours doesn't have). Considering you'd pay $20-30 for a new remote, that's most of the cost for a brand new player.