Pokemon Sword and Pokemon Shield may be near identical games but some exclusive content will set them apart. The exclusive content for the two versions will be gym trainers apparently. Both games will get Pokemon Gigantamaxing though.
Some of the gym leaders in Pokemon Sword and Shield will be exclusive to either one of the versions. In other words, regardless of which game you get, you will have trainers that are not available in the other. While it brings such exclusivity's value in question, it is good to know that owners of either game will not be undercut by lack of content compared to the other.
The information comes from the trailer embedded above. While both games will feature some of the Galar trainers, Pokemon Sword players will be able to challenge Bea, the Fighting Pokemon type expert. Pokemon Shield players will instead get Allister, a Ghost-type expert.
Judging by the background appearance in the trailer, it seems like the gyms themselves will be themed after those trainers and will probably be exclusive to their respective games. On the other hand, it's possible that just the colour palette changed depending on the gym trainer that's about to duel.
Both games will feature Gigantamaxing though. This is a new change, introduced after Dynamaxing and Mega Evolution. While Dynamaxing is available to all Pokemon and Mega Evolution is restricted to certain Pokemon species, Gigantamaxing will be available only to certain individuals of limited species.
Dynamaxing Pokemon changed their size while Mega Evolution changed their appearance. Gigantamaxing will change both, as showcased in the trailer when Alcremie turned into a massive multi-layered cake.
Gigantamaxed Pokemon will gain a unique G-Max move that is described as ultra powerful and it will depend on the Pokemon's species. Similarly, the move will replace a previous species-related move. Furthermore, Gigantamaxing will be available only on some areas of Galar so think twice before you double down on a Gigantamaxable Pokemon.