Go on with the easy steps with pictures below to get your volume icon back.
1. Check if volume icon is enabled
2. Change the text size
3. Restart explorer.exe/windows explorer
Right-click on the blank area of taskbar and choose Settings.
Click Turn system icons on or off.
Make sure Volume is on.
Go back on the window of step 2).
Click Select which icons appear on the taskbar.
Make sure Volume is enabled.
Check if volume icon is on your taskbar now.
Right-click on the blank area on your desktop.
Then choose Display settings.
Move the slider to the right to set the text size be 125% and click Apply.
After it’s done, move the slider back to the left to set the text size 100% back .
Close the window, and now your volume icon should be shown on task bar.
Open Task Manager by pressing Ctrl + Shift + Esc at the same time.
Then scroll down to find and highlight explorer.exe or windows explorer under Processes pane.
Now check if your volume icon is shown on taskbar.
That’s all there is to it.
Hopefully you can get your volume icon back.