Not that i know.

Start as tribal Novgorod, move capital to coastal county and reform as merchant republic, done.

Автор сообщения: neidhard

Does anyone know any mod that allows you to play as the Novgorod republic (preferably updated at least 5 years ago) or coverts it into a monarchy? thank you in advance!!

Though there is still no single Novgorod-enabling mod, the HIP mod has a short period where it is a republic,but while you can't select it to start, when i selected a feudal vassal first for some reason i was in-game then able to console-switch to that republic and not get a game over and play on.

Link to mod download :
https://forum.paradoxplaza.com/forum/threads/historical-immersion-project-download-faq.748775/page-245#post-29602852
There is also an invitation in that post for the discord 'server' of HIP.