i wonder why they use Chloroform as an Eluent..

chloroform's eluting power is nothing special.

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Now for cannabinoids specifically, the better option for TLC would be a mixture of Hexane and Diethyl Ether, which even allows for separation between carboxylated and decarboxylated cannabinoids, But the simplest and widely used in literature alternative  would be  methanol.

However, my suggestion would be to test your sample using the kykeon analytics  mail-in lab testing for drugs service, which would cost you pretty much the same as these Test kits of unknown Quality.

stay safe and DYOR.