Know the differences
Between Modern Sonic, Classic Sonic, and the Avatar, there are a lot of different abilities that you will have to get used to; it may be instinctual to attempt a Boost during Avatar stages, but you’ll be left flailing at nothing every time.
Modern Sonic is not only able to Boost, but can also bounce off of nearby enemies with the Homing Attack. The Avatar has their own version of the Homing Attack (known as the Wire Attack), and is armed with a Wispon that grants them various types of offensive firepower. Classic Sonic is able to Spin Dash in order to pick up speed and plow through hordes of enemies, and can also utilize Sonic Mania’s Drop Dash in order to roll upon landing.
Familiarizing yourself with the nuances of the different characters will allow you to get the best high scores and quickest times. Additionally, if you are struggling to complete one of the Avatar stages, consider equipping a different Wispon that could improve your mobility.