Eh I don't know. Try the standalone Nestopia, it's better than OpenEmu anyway

In the menu bar at the top of the screen click OpenEmu, then Settings (it might say Preferences instead if it's an older OS version). You can also bring up settings in pretty much any application on a Mac by pressing Command-comma

MacOS, right? MultiPatch https://projects.sappharad.com/multipatch/

OpenEmu → Settings/Preferences → Cores → Nestopia → Install

Good news, there is a Mac version of Gambatte Speedrun available here: https://github.com/pokemon-speedrunning/gambatte-speedrun/releases/tag/r717

You're gonna want to download "Gambatte-Speedrun-r717-psr.dmg", open it, go to your Desktop and open the "gambatte_qt/bin/Gambatte-Speedrun" disk image, then copy "Gambatte-Speedrun" to your Applications folder. After you've done that, in order to be able to run the app, you'll need to control-click it, choose Open from the menu that pops up, then click the Open button. (You'll probably see a message that says "Gambatte-Speedrun can't be opened because Apple cannot check it for malicious software." This is because the app bundle doesn't have a code signature from Apple, not because the app is actually malware or anything.)

Once it's running, use the menus up in the menu bar to change settings, open games, etc. The first time you open a game, you'll get a message about "a file you'll need to acquire before continuing." Search engines are your friend here.

Let me know if you have any questions. I speedrun on original hardware, but I do everything else on a Mac and I'm happy to help if I can