No, the DJI RS 3 Mini is not compatible with the Sony FX3.
Sony FX3 body weighs 715g (with battery+card, per Sony's own Help Guide). Paired with a Sony FE 200-600mm G OSS telephoto lens (2,115g / 74.7oz, per Sony's own spec page) -- a common real-world FX3 lens for wildlife/sports work -- combined weight is ~2,830g. DJI RS 3 Mini's stated payload capacity is up to 2kg (4.4lbs) per DJI's own product page. 2,830g exceeds that capacity by over 40%; the gimbal cannot safely balance or support this combination.
What works instead
See all compatible gimbal for the DJI RS 3 Mini →“Mass (Approx.) 715 g (1 lb 9.3 oz) (including battery pack, SD card)”
“Size and Weight 4.5 x 12.625 in. / 74.7 oz.”
“RS 3 Mini possesses a load capacity of up to 2 kg (4.4 lbs), enabling a wide range of camera and lens combinations.”
Last verified:
Confidence: high confidence