Open Spotify
Go to the playlist you want to play
Start playing the playlist
Tap the Shuffle button until Smart Shuffle is turned off
Make sure the shuffle icon is not highlighted with sparkles
On mobile, tap the Shuffle icon at the bottom of the Now Playing screen
On desktop, click the Shuffle icon in the playback controls
If Smart Shuffle keeps turning on, check the playlist settings and disable any shuffle-related playback option
Update Spotify if the option does not change properly