At 94, June Squibb gives a marvellous performance in this sentimental comedy from writer-director Josh Margolin, inspired by his own grandmother, a video of whom is played over the final credits. It is a film which is also surely inspired, more than a little, by the much tougher movies of Alexander Payne in which Squibb has also performed: she was the (late) wife of Jack Nicholson’s cantankerous widower in About Schmidt from 2002, and got an Oscar nomination as Bruce Dern’s plain-speaking wife in Payne’s 2013 movie Nebraska. I also admired her subtle, affecting performance as a woman with dementia in Stephen Karam’s strange chamber drama The Humans, from 2021.

This is quite different: a robust, slightly unreflective and unreal feelgood comedy. Squibb plays Thelma, a widow being looked after and checked in on by her slacker grandson Danny (Fred Hechinger), who is depressed at not being able to get anything like a proper job. When she is scammed out of $10,000 by a fraudster on the phone, tough Thelma sets out to track the bad guy down, riding a mobility scooter borrowed from her gentleman admirer – an excellent performance from the late Richard Roundtree. She has also borrowed a gun, of all the harmless and hilarious things, and once this item has fulfilled the destiny laid down for it by Chekhov in his dictum about what happens to guns produced in act one, it is of course entirely forgotten about.

For me there is a spoonful of sugar too many in this film, and tellingly the figure of Danny (a projection of Margolin himself) is two-dimensional, and the movie rather fudges his apparent loneliness and relationship heartbreak. Squibb is however really good: no other casting is conceivable, and it is good to see her get the lead turn she deserves.

• Thelma is in UK cinemas from 19 July and in Australian cinemas from 5 September.