I use the usepackage
\theoremstyle{plain}
\newtheorem{proposition}{Proposition}
Then I write normally
\begin{proposition} [Put name of proposition here]
...
\end{proposition}
If the name of your proposition is for example "Euler [1750] and Fermat", then TexStudio will close the name after the first ] bracket and not the last one!! Something strange will be the output. I saw that mistake, when I tried to cite like this: "\cite[][p. 99]{Serrebook}" TexStudio showed a mistake because after "\cite[]" was a cut...
Am I wrong or is that really a mistake of Texstudio?
\begin{proposition} [{Euler [1750] and Fermat}]instead of\begin{proposition} [Euler [1750] and Fermat]should result in the expected output. (Notice the extra set of{}around the proposition's name here. – leandriis Sep 20 '20 at 19:59[..]arguments, and that will behave the same way whichever editor you use, so texstudio is not related to the problem here. – David Carlisle Sep 20 '20 at 20:36