this is the site's forums not portal's forums. those are located at https://www.speedrun.com/portal_2/forum
You don't need to play Portal 2 on an emulator to use LiveSplit. You may need to make sure you have the latest version of LiveSplit and that you have correctly set up the autosplitter for Portal 2.
Here are the steps you should follow to set up the autosplitter:
Make sure you have the latest version of LiveSplit installed. Open LiveSplit and create a new layout for Portal 2. Go to the "Edit Layout" mode and click on "Control" > "Activate" next to the autosplitter. Go to "Edit Splits" and make sure you have the correct splits set up for Portal 2. If not, you can import the splits from Speedrun.com or create your own. Start Portal 2 and LiveSplit. The autosplitter should automatically start and split at the specified points. If you still can't get the autosplitter to work, you may want to check the LiveSplit forums or Discord for help. There are many helpful people there who can assist you in getting the autosplitter set up correctly.