If the warranty has expired, the repair is not worth it. Buy a new Polar and enjoy the new watch; with warranty, or buy a TOP Polar here for little coin. https://enjoy365.ch/grit-x-pro... or this one: https://enjoy365.ch/grit-x-pro... :-)

My Vantage M (almost 5 years old) has had a similar problem for a few weeks now. The top left button (illumination) no longer works. Recently, the top right button also failed.
The watch can still be used, but it's a bit awkward.

My "back button" has also been defective for a few days - and that after not even 5 years ☹️ I'm still waiting for feedback from polar customer service, but reading this, I'm probably due a new watch. But if the watches currently have such a lack of quality, then it will definitely not be a polar watch anymore! My old models worked perfectly.

Recently had exactly the same problem with this watch, also the lower left button. I contacted Polar support and was told that they couldn't even repair it because the case was sealed. At least I got a 10% voucher for a new watch. If the warranty has expired, you unfortunately have no choice but to buy a new watch.