The not-listed "stealth" Standard Range version, which previously was available only through a direct call or visit at Tesla stores, is not available for the 2021 model year, according to Electrek's sources.
Tesla still offers the SR version for the 2020 model year that's left in stock. Those cars are supposed to start at $35,000 or so (+DST), as a software-limited SRP version.
It was clear that the company was offering the Standard Range version only to fulfill Elon Musk's promise about the Model 3 for $35,000, but would like to not sell it at all.
Firstly - because the margin is lower, and secondly - because it was not viable to offer this version as it stands for only a small portion of Model 3 sales (we guess that customers were most interested in the Standard Range Plus or Long Range versions).
Because of all of that, the Standard Range version was listed in the online design studio only for quite a short time, then de-listed and now is gone completely.
With Tesla, and its constant changes in the online design studio, we never know what is coming next. It might be just a temporary change and maybe there will be some new substitute for 2020 Standard Range cars.