I downloaded the latest version of quarto from GitHub, which was supposed to fix the windows bug, but no success. I'm going to try Macos instead. I hope they fix it though since my work laptop is Windows.
I have met the same problem as yours, and I solved the two problems(a "Mojibake error" after the "create new project error" ) by copying findstr.exe and findstr.exe.mui to not only ...\RStudio\bin as the guidance of @Alencar, but also to ...\quarto\bin and ...\R-4.2.1\bin.
After all of these directories have .exe and .exe.mui, I can successully render .qmd file and create a new project!
But because my working environment is not English, I have two findstr.exe.mui files in both en-US and 'zh-CN' directory, and I don't know if the render error is caused by it.
I noticed that quarto was giving an error like "file in ' Files/Quarto/bin' not found" which made me think that it was searching for some file in its folder but failing due to the whitespace. I already reinstalled it, so dunno what exactly was is looking for I think a similar error can occur when RStudio tries to create a new project and "checks Quarto" for available templates or validates the install or something. I am on Windows 11 and have Python installed.