https://imslp.org/wiki/Main_Page
One of the biggest free score libraries.
https://www.free-scores.com/index_uk.php
https://semitony.musicaneo.com
https://www.free-scores.com/sheetmusic_a_z.php?arrangeur=tonywilkinson
Both sites are of Tony Wilkinson, a very hard-working transcriber.
https://www.vpmusicmedia.altervista.org/biblioteca.php
Another very huge site.
https://www.tabguitar.it/
a site of Luigi Borgognoni with many many Tux, Tabledit and Musescore files for guitar