How to change idea.max.intellisense.filesize if Toolbox is used?

I am using Intellij Idea toolbox for managing a couple Idea versions on Ubuntu 20. Because I work with large files, Idea is not able to completely load them, hence, some of the code is marked as red while it is being built just fine. I tried to change the idea.max.intellisense.filesize property in: /snap/intellij-idea-ultimate/309/bin/idea.properties However, it says that the file-system is read-only, so the file cannot be changed. chmod does not seem to help either. Any ideas on how to do this? Maybe there is a way to do this inside Idea itself.

If I understand right, this can help you:

https://www.jetbrains.com/help/objc/configuring-file-size-limit.html#file-length-limit

Is the same but being configured from the IDE. It worked for me, now I can see very long text files, vertical and horizontal.

Sorry if I have grammatical mistakes.