Honestly, I see this as a consequence of Sonic Mania and Sonic Forces originally not being related, the connection with the Phantom Ruby was a later addition and early on they were just very different, which explains why in Sonic Mania the Phantom Ruby is directly stated to mess up with space-time, while in Sonic Forces early script, it was all just illusions, even Classic Sonic was implied to just be an illusion triggered by Tails.
They just were totally different projects that used very different systems that had to be mixed together because they wanted to make a tie-in, which only made things confusing.
So the Phantom Ruby has a completely contradictory backstory, powers that overlap with different explanations and make no sense. Because going from both Mania, the Phantom Ruby can mess up with space-time and even be used to warp reality and travel between dimensions, while in Sonic Forces (except for the odd thing of the Null Space), it's just illusions (except it can still cause dimensional travel because... they changed the original plot as originally Classic Sonic was an illusion).