how can i get plugins for gedit for zooming the text file?

If gedit has missing plugins, make sure you have the gedit-plugins installed.

sudo apt-get install gedit-plugins

After that, (you probably need to restart gedit) you will have a plugin called "Text Size".
Make sure the plugin is enabled, and you will be able to "zoom" (i.e. change font size) using Ctrl + Mouse Wheel.

This is the list of plugins available in the gedit-plugins package

$ apt-cache show gedit-plugins
[...]
 The following plugins are included:
  * Git: Git differences
  * Bookmarks: Easy document navigation with bookmarks
  * Bracket Completion: Automatically adds closing brackets.
  * Character Map: Insert special characters just by clicking on them.
  * Code comment: Comment out or uncomment a selected block of code.
  * Color Picker: Pick a color from a dialog and insert its hexadecimal representation.
  * Color Scheme Editor: Source code color scheme editor
  * Commander: Command line interface for advanced editing
  * Dashboard: A Dashboard for new tabs
  * Draw Spaces: Draw Spaces and Tabs
  * Git: Git differences
  * Join/Split Lines: Join several lines or split long ones
  * Multi Edit: Edit document in multiple places at once
  * Smart Spaces: Forget you're not using tabulations.
  * SyncTeX: Synchronize between LaTeX and PDF with gedit and evince.
  * Embedded Terminal: Embed a terminal in the bottom pane.
  * Text Size: Easily increase and decrease the text size
  * Word Completion: Word completion using the completion framework
[...]

SOME WAYS OF FIXING:

1. $ sudo apt-get install gedit-plugins -y

Go to gedit preference > plugins and activate what you need.

If text size doesn't appear , so :

2. googling : Looking for gedit plugin text size . I found this : https://packages.debian.org/buster/gedit-plugin-text-size .

   Package exist .

   *** and do this :

   $ sudo apt-get install gedit-plugin-text-size   -y 
   

   Then reopen gedit: preference > plugins. You'll see "text-size" appear.

( THIS WORKED FOR ME ) .