That might be a problem with your tooling, but most likely not. I know how to do that in Linux (XCompose) and I've heard there are similar tools in both Windows

That might be a problem with your tooling, but most likely not. I know how to do that in Linux (XCompose) and I've heard there are similar tools in both Windows and MacOS as well. So more likely just a problem of not being aware/proficient with using these tools properly. Typing λ² is 6 keystrokes for me, no touching mouse required. And while maybe not very illustrative in this post, I'd argue it's way more readable than lambda_squared when being a part of long and complex formula.