If location scouting is taking place in the Scottish Highlands in December, this means that the area will be covered in snow during this time. This could indicate that the film will be taking place, at least in some part, on some sort of ice planet.
According to The Daily Record via GamesRadar, a source close to the publication said that three days of shooting would be taking place in Scotland for the Taika Waititi-helmed Star Wars film. Information was obtained from The Daily Record, which mentioned that the shoot was due to take place in December.
As noted by GamesRadar themselves, the two most prominent snow planets to be featured in Star Wars canon are Hoth and Ilum. Though a specific era has not been defined for the film, it could be interesting for the film to delve into the impact that the Galactic Civil War had on Hoth after the events of The Empire Strikes Back. Alternatively, the film could go into more of the history of the planet pre-Empire, perhaps following a civilization that existed there beforehand.
It should be noted that GamesRadar speculates that it is unlikely that this will be proper filming, instead acting as location scouting for the film. As Waititi is currently in pre-production for this Star Wars project in addition to Thor: Love and Thunder, it is likely that it is far too early for production to begin.