That, fortunately is the exact issue mentioned in the post above. Will look into the GX games thing but with the windows launcher if you implement the fix in the link in my previous post, or get the newest files it will fix that particular error. The mention of " if (_option[0] == "Attack") return 99;" is the giveaway.
I got an error when I interact with the slimes:
___________________________________________
############################################################################################
ERROR in
action number 1
of Create Event
for object oBattle:
argument 5 needs to be a struct
at gml_Object_oBattle_Create_0 (line 37) - enemyUnits[i] = instance_create_depth(x+250+((i mod 3)*10)+((i div 3)*25),y+68+((i mod 3)*20),unitDepth,oBattleUnitEnemy,enemies[i]);
############################################################################################
gml_Object_oBattle_Create_0 (line 37)
gml_Script_NewEncounter (line 3)
gml_Object_oSlime_Collision_oPlayer (line 3) - NewEncounter(choose([oBattleUnitSlime,oBattleUnitSlime],[oBattleUnitSlime]), sBgField);
You seem to have a mix of versions here for some reason. Line 37 of your oBattle creat event is from the new version, but the line in your slime collision event is from an old version.
Edit: i've also confirmed that the most recent version also works properly in Opera GX, so if you're still hitting errors this is a problem with your project specifically.