Rav Hutner says that the foundational issur of lashon ha'ra is judging unfavourable (dan le'kaf chov).
The lashon ha'ra is an expression of the negative evaluation that you have attributed to the person whom you have judged unfavourably.
So the basic issur of lashon ha'ra is to construe someone else as having negative value.
Judaism isn't as overtly focused over negative thoughts like some other religions are. The Christians follow a Rabbi who says that someone who murders in their heart or commits adultery in their heart is guilty of the actual thing. Judaism as a whole is not willing to take this stance. Thinking about murder is definitely different than murder itself, since ...
I would like to elaborate the Passuk in Isaiah above (9,16),
עַל־כֵּ֨ן עַל־בַּחוּרָ֜יו לֹא־יִשְׂמַ֣ח׀ אֲדֹנָ֗י וְאֶת־יְתֹמָ֤יו וְאֶת־אַלְמְנוֹתָיו֙ לֹ֣א יְרַחֵ֔ם כִּ֤י כֻלּוֹ֙ חָנֵ֣ף וּמֵרַ֔ע וְכׇל־פֶּ֖ה דֹּבֵ֣ר נְבָלָ֑ה בְּכׇל־זֹאת֙ לֹא־שָׁ֣ב אַפּ֔וֹ וְע֖וֹד יָד֥וֹ נְטוּיָֽה.
Therefore the Lord will take no pleasure in the young men, nor will he pity the ...