The streamlabs option you mention is not something that does what you think. That is a set of built-in presets for output settings at each of those resolutions. That has nothing to do with what twitch does on their end.
Transcoding options on twitch (as in, the drop-down your viewers can select) is given on availability basis. Partners are guaranteed to get it, with affiliates and non-affiliates getting it as available.
The point at which this is determined is at the start of stream, so it is possible to try starting/stopping stream until you see that you've been given transcoding options. This is usually a lot more reliable to do in low traffic hours, but your mileage may vary.