Force nested loop over observables to wait for all

I've read about forkJoin, async, await, and also tried out angular life cycle methods, but finally found no good solution.

I need to wait until initiAttributesMap has finished his job before next code lines run. If I use a setTimeout I get the map fully filled. But I want to avoid setTimeout. Thank you.

somewhereInCode (){
    initAttributesMap();        
    setTimeout(() => {
        //do Other things                
            }, 20);
}

public initAttributesMap(bObjects: BObjects[], attributesMap: Map<string, string>){
    bObjects.forEach( (bObject: BObjects) => {
        if ( bObject.cValues !== null ) {
            bObject.cValues.forEach( ( cValue: CValue ) => {
                this.myService.getValueTypes( cValue.source).subscribe(
                        ( possibleValues: PossibleValues[] ) => {                                
                            let displayName = possibleValues.find( foundValue => cValue.id == foundValue.id ).displayName;
                            attributesMap.set( cValue.attributeName, displayName );
                        } );
            });
        }
   });

}

If you want wait while all attributes will be initialized:

somewhereInCode (){
  initAttributesMap().subscribe(() => {
    //do Other things
  });        
}

public initAttributesMap(bObjects: BObjects[], attributesMap: Map<string, string>){
  const resObs: Observable<unknown[]> = []
  bObjects.forEach( (bObject: BObjects) => {
    if (bObject.cValues !== null) {
      bObject.cValues.forEach( ( cValue: CValue ) => {
        const obs = this.myService.getValueTypes( cValue.source).pipe(
          tap(( possibleValues: PossibleValues[] ) => {
            let displayName = possibleValues.find( foundValue => cValue.id == foundValue.id ).displayName;
            attributesMap.set( cValue.attributeName, displayName );
          })
        )
        resObs.push(obs);
      });
    }
  });
  return forkJoin(...resObs);
}