Brightness adjustment interval in windows

I have a windows laptop in which we can use the Fn+Arrow Key to change the brightness of the screen. The default interval of brightness interval is 10%.

Is there any way I can reduce this interval so I can fine tune the brightness instead of changing brightness at a step of 10% at a time.

There is a slider in power option which is very nice to fine tune brightness, but I want to do it with shortcut not want to go to power-option every time.

Is there anything I can do about this issue something like changing registry or some other software or something other solution?

By default this is the best you can get. However, there are utilities that can help you achieve what you're asking. This answer shows how to configure hotkeys to adjust brightness using NirCmd.

Paraphrasing with adjustments to meet your needs:

You can also create shortcuts with keyboard shortcuts to NirCmd, and in the Target field specify parameters such as changebrightness <level> (where level can be +ve or -ve). The following commands will even automate the creation of the shortcuts for you (edit as required):

nircmd.exe cmdshortcutkey "~$folder.desktop$" "Decrease Brightness" "Ctrl+Alt+F9" changebrightness -1

nircmd.exe cmdshortcutkey "~$folder.desktop$" "Increase Brightness" "Ctrl+Alt+F10" changebrightness 1