private Boolean: BehaviorSubject<boolean>;

export class getDivStatus {
public getTheBoolean(): Observable<boolean> {
    return this.theBoolean.asObservable();
}

public setTheBoolean(newValue: boolean): void {
    this.theBoolean.next(newValue);
}
}

My component

...
import {getDivStatus } from /getDivStatus.service.ts
...

export class divCom implement oninit {
constructor(private divservice: getDivStatus)
ngOnInit() {
booleanDiv = true;
this.divservice.setTheBoolean(true);

if(anotehrcondition) {booleanDiv = false; this.divservice.setTheBoolean(false);}

}

app.compoennt.ts

import {librarytotest} from librarytotest;

@compoennt({
...})

export class AppCompoet implements oninit{
ngoninit() {
this.librarytotest.getboolean().subscribe({x => console.log(x)});

}
}