Despite GT utilizing iconic Dragon Ball characters, it has never received fan acceptance as an official part of the series.
The long-standing debate within the Dragon Ball community about whether Dragon Ball GT is canon or non-canon finally has an answer. Shueisha, the manga publisher, disclosed this in 2017 during the Dragon Ball Tenkaichi Budokai event.

Released in 1996, Dragon Ball GT was initially considered an unofficial sequel to the concluded Dragon Ball manga. Produced by Toei Animation, Dragon Ball GT is the third anime series in the Dragon Ball franchise and serves as the successor to Dragon Ball Z.

Author Akira Toriyama played a crucial role in laying the groundwork for the series and creating rough designs for most characters in GT. However, the Super Saiyan 4 form was not designed by Toriyama. Additionally, the Dragon Ball author did not draw the logo, title each episode, or oversee the production.
According to many fans, Dragon Ball GT is an 'unofficial' anime due to the lack of direct involvement from Akira Toriyama in the script and content, with Toei Animation being the driving force behind it.
With the debut of Dragon Ball Super, following an entirely different timeline than GT, fan debates have once again surged.

Thanks to fan-dedicated accounts like @DBGTLegacy, scenes from the 2017 event have reappeared, showcasing the official Dragon Ball timeline provided by Shueisha. To everyone's surprise, not only do Dragon Ball, Dragon Ball Z, and Dragon Ball Super appear, but also Dragon Ball GT. This is because Super takes place immediately after the end of Z, while GT is set five years later, maintaining a divergent timeline.
Akira Toriyama, the creator of the franchise, referred to GT as a 'small part in the history of Dragon Ball.' His involvement in various aspects of GT's production has reinforced this statement. Perhaps the most reasonable explanation is that GT unfolds in a parallel universe, a concept introduced in Dragon Ball Super.
So, it's time to accept, following the timeline and the official statements from Shueisha and Toriyama, that Dragon Ball GT is canon. At least, this holds true until proven otherwise.