Check the betas tab under Stardew Valley's steam library properties. Make sure you're not using one of the older compatibility options.

Originally posted by Buffmania:

Check the betas tab under Stardew Valley's steam library properties. Make sure you're not using one of the older compatibility options.

i check it before i up this help bro, i set it to none and just 1.6.14 =((

You could probably manually download the depot to get things working. It's a bit complicated, but there's instructions here:
https://www.gog.com/forum/general/guide_how_to_download_older_versions_of_a_game_on_steam
and the Stardew steamDB page is here:
https://steamdb.info/app/413150/depots/

I haven't used this method in a while, but it should still be up to date. If you need more help i'd suggest searching the net for a more in-depth video about manually downloading steam depots.