[gujal]

ensure to have at least python version 3.7 or above

Not that easy with Ubuntu LTS, without breaking stuff. AFAIR, I can break system to the point it won't boot - and just installing it side by side won't work as apps won't pick up default Python installation.
Is it necessary to use that version of Python for building plugin? If it is, I'll have to reinstall whole system to have newer updates.

Yes, that is why I suggested to move to Ubuntu 20.04 LTS.
Kodi 19 works on Python 3.7.5 or above 3.6 or above (Thanks Fuzzard) and on Windows and Android comes with 3.8.5. On linux it relies on System Python and with Ubuntu 18.04LTS stuck at Python 3.6 can't do much. SO if you want to use Ubuntu 18.04LTS, then stick with Kodi 18.9 and if you want to move to Kodi19.x move to Ubuntu 20.04LTS first