Smalltalk environments have defaulted to proportional fonts back to the beginning of time [1]. Some of the newer ones allow for richtext code, so if you really need to make that ascii art drawing, you can change the font in the comment. Also look up elastic tabstops for an alternate alignment solution.

The tricky part is there aren't many proportional fonts designed for coding (but more than there used to be). One early 90s version of ST defaulted to Helvetica, which was a nightmare to read on the then current lowres screens. Of the current choices, Input is probably the best place to start. Verdana is popular with some, and I've used Lucida a bunch, both sans and serifed. I have also had fun using not really suited display fonts like Papyrus or surprisingly readable drafting handwriting fonts like Tekton. It is usually recommened to use a sans font for readability, but I think that advice is outdated on modern very hires displays with subpixel antialising.

[1] https://fontstruct.com/fontstructions/show/1693628/cream-10p...

The proportional fonts question recurrs periodically:

2005 https://ask.metafilter.com/16469/Proportional-programming-fo...

2010 https://slashdot.org/story/130020

https://www.quora.com/Are-monospace-or-proportional-fonts-be...

2019 https://news.ycombinator.com/item?id=18958046