At least as of R2019b, saveas() and print() do not accept uifigure handles. The documentation suggests that's still the case, but my network connection is too crappy to open MATLAB online to verify that.
Documentation suggests that exportgraphics() should accept uifigure handles, but again, I cannot test that. It should support PDF outputs as well. Depending on what you're doing, maybe exportapp() is appropriate.
As always, using JPG for anything is usually a completely bad idea. For synthetic graphics with hard edges and flat coloring, JPG will produce a visually conspicuous degradation of image quality, and the file size will typically be larger than a PNG. Unless you understand what compromises come with a 70% 4:2:0 JPG, don't use JPG.
