The High Republic initiative has confirmed two new Jedi Grandmasters in Star Wars canon, which means Yoda is no longer alone. The concept behind ranks in the Jedi Order has been in flux since the original trilogy released, and it wasn't finalized in the true continuity until 2020. It was revealed in A New Hope that there were Jedi Knights, then later came the Jedi Padawans and Jedi Masters, but the idea of Jedi Grandmasters being one of the ranks wasn't always a thing in Star Wars.
In the Legends continuity, Jedi Grandmasters - typically the most senior Jedi and who is considered to be the head of the Order - were prominent throughout the history of the Jedi Order, including in the one Luke Skywalker founded after Return of the Jedi. But in canon, the only person known to be a Jedi Grandmaster was Yoda. It made sense since he had been the oldest and wisest Jedi on the Council, not to mention had trained thousands of Jedi over the course of hundreds of years. As it turns out, though, he wasn't always the only Grandmaster.
Lucasfilm's The High Republic has officially launched, and two new Jedi Grandmasters have been revealed within it: Lahru and Veter. Lahru is name-dropped as a Jedi Grandmaster in the novel Light of the Jedi, whereas Veter is mentioned to hold the rank in The High Republic #1 comic book. Not much is known about them yet, but Light of the Jedi does state Lahru convened the Jedi Council to discuss the Nihil threat, who are the villains of the new era.
What's interesting is that The High Republic doesn't just confirm one new Jedi Grandmaster but two, which could change how fans perceive the rank. Given that the new era is set hundreds of years prior to the prequel trilogy and is meant to showcase the Jedi in their prime, it's possible the Jedi Grandmasters of the time carried out different responsibilities - which Yoda took on himself during the prequel era, which is now known as the Fall of the Jedi.
All in all, though, having three Jedi Grandmasters is more in line with what the Jedi are meant to be. Sure, the Jedi Council ruled as a collective body, but Yoda and Mace Windu had much more power than the rest of the Jedi Masters. Having two other people at the same rank as Yoda would allow the Jedi to rule more like a committee. Considering what happened to the Jedi when Palpatine came to power, moving away from their roots and more towards an authoritarian body is partially responsible for the Jedi's downfall.