It depends of DPI. When high DPI is selected, PSPad will use bigger version of icons. When you change it and save settings (icon sets for menu and toolbar are customizable in the PSPad settings), PSPad will remember it for this computer and won't change it.
If you have portable PSPad and you will run it on different compouters, on the computer with high DPI, PSPad will use bigger icon size. -- <https://forum.pspad.com/read.php?4,71403,71404> PSPad freeware editor https://www.pspad.com
