Sorry, i just saw the message. It should work in dosbox-x. If not, try dosbox staging (i have 0.81.0 from my Linux distro and works here).
Make sure CPU cycles are set to auto or max and the CPU core to dynamic, though these should be the default.
Aside from that, decompressing Petra99o.zip to some directory like C:\PETRA and running PETRA.EXE should be fine (you don't need the SB16 patch for dosbox). Might want to try CONFIG.BAT to configure audio to match the SB16 settings in dosbox.conf.