This is really happening at the font level (as @hoelk mentioned) — RStudio is just doing a better job of rendering the fonts (or really, the new Chromium-based rendering engine is allowing support for the ligatures that were in the fonts all along).
These "programming ligatures" are definitely a matter of taste (here's Fira Code's case in favor) — some people like them so much that they hack them into fonts that don't support them natively!
While I agree they might be confusing for a brand new person, I don't think that a fresh RStudio installation uses a font with programming ligatures (happy to be corrected on that — I don't have a fresh install of RStudio handy!), and I suspect most brand new people are going to use the default font (or something super common like Consolas, which does not have programming ligatures).