It looks like you solved the problem by installing Arabic font.
In one post (Can I Add External Fonts In Shotcut) I read that Shotcut uses the fonts already installed on the PC (I have an Arabic-based font installed).
In another post (How to include new fonts?) it says that an html file should be set up using a text editor:
“The filter ‘Overlay HTML’ allows you to load an HTML file as a ‘text’ filter over a video. If you know how to create an HTML file and load your font in that, then it should be compatible with Shotcut using Overlay HTML.”
Please advise on how you installed Arabic font. (Again, even though an Arabic-based font is already installed on my PC, I still have the LTR problem.)