You have found it, the classic Jarkey or Jarpop jar opener.

Just attach to the rim of a jar and lever slightly, the vacuum seal which is causing the lid to be on so tight is released from the jar and the jar opens easily.

There are lots of jar openers on the market, even robots, all at different, sometimes surprising prices.

It is amusing when the simple low cost classic Jarkey or Jarpop generally does the job.