I do not understand how to download and install the plug-in
resynthesize in Gimp 10.
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Regardless I have found this post which states you only need to run:
sudo apt install gimp-plugin-registry
This will install many useful Gimp plugins automatically, including resynthesize.
Here's a simple guide:
Enter the command
sudo apt install gimp-plugin-registry (it is case sensitive so make sure that's right).
Press enter and it will ask for your password, enter that and press enter. While you are typing the password the terminal will not change.
The plugins will then install, once it's finished you can close the terminal.
If you re-open Gimp you can see the plug-in installed in the plug-in browser.