As indicated in the comments, what you have to do is use Get Raster Properties. I am familiar with your problem of using the parameter obtained from this tool. Here you can find a similar solution with Raster Calculator. However, I find it simpler to use the Create Constant Raster tool to create constant rasters with their values equal to the mean and standard deviation of your input raster and then do calculations based on that:
There are two connectors from Input raster to Create Constant Raster, these are for the output extent and the output cell size. Then, the mean+ 2xStdev is calculated with Times and Plus for the rasters. Then, you can use a Greater than Equal (or Less than Equal, whichever you need) to yield the final thresholded raster.
Note that this is designed for a binary threshold as you describe.