uPyCraft is a IDE runs on Windows and Mac, designed with simple interface and it is convenient to use.
To provide an easy and practical platform for fans of MicroPython, uPyCraft has many internal basic operation libraries.
Today I downloaded the uPyCraft IDE, first v1.0, then v1.1 (on Win10)

When I run the program I get "Please install SourceCodePro font" - with OK and Cancel. Neither seems to do anything remarkable. Neither option fixes the problem.

I went and got the font from here: https://fonts.google.com/specimen/Source+Code+Pro
I installed the 7 TTF files. The font shows ok in the Windows Control Panel etc.

No change - the IDE still complains when it loads up. When the IDE does come up it seems to display the menu options etc using the SourceCodePro font... as ugly as it is. So why is the program still complaining?

It is not a deal killer but it is annoying and I hate jumping through hoops only to find it is all for nothing (and then of course I had to create yet another online account for this forum to post this silly question - sheesh.)
You can try https://upfonts.com/liberator-font/ if you need some nice fonts. Presentation requires the use of easy-to-read fonts.
Your text will be more valuable because of the fonts. It aids readers' comprehension of text material. The right combination of color, font and text size might help you attract your target audience. That's a good selling point, and even in marketing, each font is picked very accurately. Big companies are paying big money to get fonts that they can use for the future in their campaigns.
I agree with the above that fonts are of great importance for influencing perception. Your problem may be due to the wrong font, try changing it. Look at MasterBundles there are many cool modern font options and many more cool website design ideas, this source will clearly be useful for one purpose or another.