MuseScore is a good source! But there is absolutely an art (with deeply mathematical influences) to producing pleasant-to-read sheet music. You’re better off paying for even mediocre songbooks, say Hal-Leonard or Alfred press, for musicians or even just genres you like, than sticking purely to free sources. For $5-20 a book (of say, 8-20 songs) I would argue it’s better to pay for it.