Fix tiny Khmer font size on Telegram for desktop
Go to Run App in your computer
Then typing Regedit and click ok button

Copy (HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\FontSubstitutes) and Enter

Find MS Shell Dlg 2 then right click to Modify and change value data to khmer font

For example: Khmer MEF1, Khmer OS,ect.
Then restart your computer