If you want above-mentioned functionalities update to 2021.
but I'm already using premiere pro 2021, version is 15.2.0
Background needs to be set to translucent and a color.
You cannot edit font size: it is set to standard size for broadcast.
If you want plain subtitles set caption to Subtitle instead of 708.
Right click on tracker header > track settings
If I want to change the size, which one should I choose?
I want to be able to customize my captions.
I think I found the answer.
I changed the caption to Subtitle, and I'm able to edit it. Thanks.