Yes, endless mode seems to be gone. Neither F12 nor playing through the game works.
At the moment I'd suggest downloading the older version of the game, I've made both the 2020 and 2021 version of the game available. I know this is inconvenient, but upon making the update several things seemed to change. (Namely, all customers are now clothed entirely in white, and Endless Mode has gone astray.) Further updates might compromise stability further.
But I'm the sound / story guy, I could be wrong! If there's another update we'll definitely make a post. (Currently locked into Burger Farm development.)
Cheers,
Scythe Dev Team
3 years ago(+1)
The 1 GB file that isn't the 2021 Update is the original release that still features endless mode.