Great news! Now you could stick with portable mode or you can investigate further to try to find out how you can resolve the slowness issue when in non-portable mode. It's up to you.
When you are in non-portable mode, the Arduino IDE is accessing two external folders:
Sketchbook: The location is set in File > Preferences > Sketchbook location. When in portable mode, the default location of the sketchbook is {Arduino IDE installation folder}/portable/sketchbook. When in non-portable mode, the default location of the sketchbook is something like C:\Users\{user name}\Documents\Arduino, but it might be different if you have OneDrive enabled.
Data folder: When you are in portable mode this is located at {Arduino IDE installation folder}/portable. When in non-portable mode it is located at C:\Users\{user name}\AppData\Local\Arduino15.
So the next step in the investigation would be to determine which of those two folders were the cause of the slow down. The way you can do this is:
- Delete the portable folder
- Start the Arduino IDE
- File > Preferences
- Note the folder shown after "Sketchbook location".
- Click the "OK" button.
- Close the Arduino IDE
- Create the portable folder
- Start the Arduino IDE.
- File > Preferences
- Set "Sketchbook location to the location of the sketchbook when in non-portable mode.
- Click the "OK" button.
- Close the Arduino IDE.
- Start the Arduino IDE.
After doing that, there will likely be two possible results: If the Arduino IDE is still fast then you know that the problem is with the location of the data folder when not in portable mode. If the Arduino IDE is slow then you know the problem is with the location of the sketchbook folder you set in
File > Preferences > Sketchbook location.