A terminal can display strange symbols after a command changes its state or binary data is displayed as text. GNOME Terminal provides a reset action, but one of its reset choices also removes the scrollback you may need for diagnosis. Choose based on what you need to preserve.

Keep the context first

Note the command or action immediately preceding the display problem. If readable output remains, preserve the important error lines in a local note. Record whether you know the command has finished or whether it may still be running.

Do not type a series of repair commands into an unreadable session. If an important operation may be active, use another known-good terminal or ask support to inspect its status. A broken display is not enough evidence to interrupt a database operation or software update.

Once the foreground command is finished or safely dealt with, open GNOME Terminal's menu and choose Advanced, Reset. GNOME documents this as resetting the terminal screen state. Check whether text and cursor behaviour become readable again; when appropriate, press Enter to obtain the shell prompt.

Clear only when clearing is intended

Advanced, Reset and Clear adds another action: it clears the visible screen and scrollback contents. Use it only after preserving any output you still need. It cannot serve as an evidence-preserving alternative just because its name sounds more thorough.

After the reset, perform a harmless check such as displaying the current directory. Verify that you can read the prompt and newly produced text. Keep the original failure separate from this display test; a readable terminal does not prove that the preceding command completed its work.

If the same program repeatedly garbles the terminal, document a minimal reproduction and the terminal version for its maintainer. Include whether resetting the display helped and whether the program itself completed. This narrows the report to terminal behaviour without presenting a visual reset as a repair of the underlying task.

Sources: GNOME documentation.