There is the alphabet called IAST for Sanskrit transliteration (to input the diacritics, special accents, etc).
How can we type the diacritics in LibreOffice?
Character input is basically a matter of operating system rather than an office suite. Thus, consult the respective manual.
Find a keyboarding solution such as https://keyman.com/ that has the characters you need. This is for any application on your system, not just LibreOffice.