The season pass is an incredible deal and it’s prorated to half price right now. There a ton of extra content that comes with it too. I know that’s not the answer you are looking for, but honestly the quality of the broadcasts is better than anything fox sports, Ballys, or espn have ever put out. Well worth it in my opinion. If you have T-mobile as a carrier, or are a season ticket holder to any team in the league, you can get it for free. If you are already an Apple TV+ subscriber you can get it a bit cheaper too.
More to your actual question though, some games are free on Apple tv weather you have a season pass or not. Additionally some games are simultaneously broadcast on FS1 or over the air on Fox or other channels. The MLS app should tell you if there are additional channels the game is going to be broadcast on. Lastly I’m sure there are other method should you choose to sail the high seas, but in my experience the quality is never really good, and most of those sites are cancer for your device.
Yeah MLS is exclusive to Apple plus now except for the games that are on free local channels like Fox, ABC, etc. There's no other way to (legally) stream the games.
I’m including all ways to stream; if it’s an Apple exclusive then I haven’t found any way at all to stream. I went ahead and paid the $ to Apple and have enjoyed seeing the games live, without having a mad google session as the game began with a gazillion porn ads on sketchy sites to find the SkySports stream or wherever it would be available in previous years.