Thank you @ariehen for your reply.
Was that.
For some reason, before I did not have this “issue”.
On Windows 11, the default monospace font for Obsidian was Cascadia Code, and this one has ligatures.
I changed it to Consolas (the same used by VSCode and Notepad), and now I don’t have ligatures. Same as it was before.
Now, on “Live Preview” looks like this:
And on “Source”, like this:
Thank you all.