Sonic Frontiers PC speedruns are ranked according to Load Removed Time, or LRT.
To set this up:
Download and open LiveSplit.
Set up LiveSplit to your liking, according to one of the many tutorials you may find online.
Right click the LiveSplit window, then click "Edit Splits".
Type "Sonic Frontiers" in the game name, and the autosplitter and its related settings should show up.
Enable the autosplitter, and go into its settings to check the spots in the run where you want the game to split automatically.
Make sure to look at the Misc. tab too, as it includes some really useful checks like unlocking skills and collecting music notes.
Ensure the timer in your layout is set to "Game Time" rather than "Real Time".
Note: The check for White Emerald on Ouranos Island does not work since v1.20.
Use "Open The Final Door (After The Second Hacking Minigame)" instead.
Shoutouts to Jujstme and Labrys for making the autosplitter.
Console speedruns are ranked using real time (RTA), as there is currently no way to remove load times from these.
Most Sonic Frontiers speedrunners have subsplits on their layout.
This is what allows them to have, in any% as an example, one bigger split for each island and smaller splits for each section within that island.
This video explains how to set them up: