I've just upgraded to zsh using the following tools:
This is the problem I'm experiencing:
I am using the following ITerm2 configuration:
BTW I've already tried to install the Powerline fonts
What you've highlighted in the screenshot is prompt. Zsh prompt is controlled by themes. The theme you are using is apparently Powerlevel10k (your questions says "Powerline10K" but that's almost certainly a mistake).
So you'd like to see powerline glyphs in Powerlevel10k prompt in iTerm2. To do that you need to type p10k configure
. It'll immediately ask whether you want to installed the recommended font. Say "yes", then restart iTerm2 when prompted, and then again run p10k configure
. This time it won't offer to install a font and will present you with the choice of prompt styles, some of which use powerline glyphs.