This is because data inside subscribe() is of type Array<CountryInfo[] | VariableInfo[]>. So referring to the array with the index data[i] infers the type CountryInfo[] | VariableInfo[], hence the error.

You can use array destructuring to have more specific types, which should fix the error.

forkJoin([countries$, floors$, memberTypes$, categories$, businessTypes$, voterRelations$, bloodGroups$, designations$])
.subscribe(([countries, floors, memberTypes, categories, businessTypes, voterRelations, bloodGroups, designations]) => {
    this.countries = countries;
    this.floorLists = floors;
    this.memberTypes = memberTypes;
    this.memberCategories = categories;
    this.businessTypes = businessTypes;
    this.voterRelations = voterRelations;
    this.bloodGroups = bloodGroups;
    this.designations = designations;
});

I think you can achieve that using another overload of the forkJoin, because the one you're using requires the observable array items to be from the same type.

The following overload should works:

forkJoin({
  countries: countries$,
  floors: floors$,
  memberTypes: memberTypes$,
  categories: categories$,
  businessTypes: businessTypes$,
  voterRelations: voterRelations$,
  bloodGroups: bloodGroups$,
  designations: designations$,
}).subscribe((data) => {
  this.countries = data.countries;
  this.floorLists = data.floors;
  this.memberTypes = data.memberTypes;
  this.memberCategories = data.categories;
  this.businessTypes = data.businessTypes;
  this.voterRelations = data.voterRelations;
  this.bloodGroups = data.bloodGroups;
  this.designations = data.designations;
});

ForkJoin with a Dictionary instead of an Array

Positional arguement in an array are fairly error-prone. ForkJoin lets you solve this problem and the problem with types in one fell swoop. As long as the keys match, you can re-order the inputs without fear. It also stops you from re-typing the names over and over and over again.

forkJoin({
  countries: this.countryService.getCountryLists(),
  floorLists: this.variableService.getFloorLists(),
  memberTypes: this.variableService.getMemberTypeLists(),
  memberCategories: this.variableService.getMemberCategoryLists(),
  businessTypes: this.variableService.getBusinessTypeLists(),
  voterRelations: this.variableService.getVoterRelationLists(),
  bloodGroups: this.variableService.getBloodGroupLists(),
  designations: this.variableService.getDesignations()
}).subscribe(data => {
  for (const [key, value] of Object.entries(data)) {
    this[key] = value;
  }
});

Of course, the obj here can be pulled out of the forkjoin and built (incrementally or otherwise) elsewhere. In this case make sure you type "callListType" properly somewhere so your code knows what to expect (Is voterRelations an optional field are there numerous types at play?)

let callList: callListType =  {
  countries: this.countryService.getCountryLists(),
  floorLists: this.variableService.getFloorLists(),
  memberTypes: this.variableService.getMemberTypeLists(),
  memberCategories: this.variableService.getMemberCategoryLists(),
  businessTypes: this.variableService.getBusinessTypeLists()
}
callList = {...callList, voterRelations: this.variableService.getVoterRelationLists()};
callList.bloodGroups = this.variableService.getBloodGroupLists();
callList["designations"] = this.variableService.getDesignations();

forkJoin(callList).subscribe(data => {
  for (const [key, value] of Object.entries(data)) {
    this[key] = value;
  }
});