I’ve been playing with Windows 3.x on Dosbox and Dosbox-X – the S3 drivers found on Vogons have not worked for me.
I don’t know if these work, but it is possible to get the original first party S3 drivers via archive.org: https://web.archive.org/web/20090611100530/http://www.s3graphics.com/en/drivers/legacy_software_archive.aspx#id_765drv
Now also mirrored at https://cubiclehermit.com/w9524107.zip in case archive.org goes back down.