How do I make my phone stop starting in charge only mode when I plug it in? I did something with developer mode and now whenever I plug my phone in it wont let me access the files until I pull down the task bar and tap on "Charging via USB" which brings up a window where i can change it to "Transfer files". But I have to do this every time and it's so annoying that I basically don't transfer files to/from my phone any more.

In settings > system > developer options I disabled USB debugging, but it didn't seem to change anything.
At least on my device, it is a default behavior and cannot be altered. It was brought in with Android 8 and is same on 9 and 10.
The default USB connection mode is always charging. You need to manually enable the file transfer mode when needed.