I have no idea why Chelsea want to extend Jackson's contract when his performance isn't that good lol.
Chelsea will be in loss I guess, there's no team want Jackson except Chelsea release him cheaper than his market value. It's really rare to see old players in Chelsea, Jackson will turn 31 in the next 9 years, 31 years old striker in Premier League mostly can't compete with the young players anymore.
Jackson is good striker mate, he only lack consistency and Enzo Maresca believes in him and he wanted to change him to a better striker which I am sure will be possible because the team have no any other reliable striker than him since they couldn’t sign Victor Osimhen from Napoli, they have to coach Jackson to help the team to be competitive by scoring goals for them.
Extending Jackson’s contract will be of benefit for Chelsea, they are hoping for him to step up his performance this season, if they are able to achieve that, he will be a striker that many teams will be coming for especially if Chelsea signed Osimhen or any other big striker probably next season. A release clause will help Chelsea to get some good amount of money from the player instead of leaving the team for free maybe when his contract expires.