For ST/STE -only programs, only options for freely scaling the window is SDL2 build of Hatari 2.x.
Note that when running ST/STE games on Falcon, they can work better if you run first a program that:
* disables 030 caches
* sets Falcon to STE bus compatibility (0xff8007 register) & 8Mhz mode (8Mhz you can force from Hatari options dialog too)
Unless they're GEM programs, you should run them from ST compatible video mode (selectable from GEM desktop).
You can also check whether there's a version of your game that has been fixed to work on Falcon etc.
Because ST/STE games don't use DSP, you can speed up Hatari Falcon emulation a lot by disabling DSP emulation from Hatari options.
And if you want TOS to boot (a lot) faster, use latest EmuTOS instead of TOS v4. While many Falcon programs need TOS v4, ST/STE programs that work from a (GEMDOS) HD, should work also with EmuTOS.