To resolve this issue, you can modify the directive to include a unique identifier for each instance of the directive. One approach is to use the NG_VALUE_ACCESSOR provider and provide a unique useExisting value for each instance. Here's an updated version of the UppercaseDirective that addresses this problem:

import { Directive, HostListener, forwardRef } from '@angular/core';
import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';

let nextId = 0;

@Directive({
  selector: '[appUppercase]',
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => UppercaseDirective),
      multi: true
    }
  ]
})
export class UppercaseDirective implements ControlValueAccessor {
  private onChange: (value: any) => void;
  private onTouched: () => void;
  private id = `appUppercase_${nextId++}`;

  @HostListener('input', ['$event.target.value'])
  onInput(value: string) {
    const transformedValue = value.toUpperCase();
    this.onChange(transformedValue); // Update the FormControl value
    this.onTouched();
  }

  writeValue(value: any): void {}

  registerOnChange(fn: any): void {
    this.onChange = fn;
  }

  registerOnTouched(fn: any): void {
    this.onTouched = fn;
  }

  get controlId(): string {
    return this.id;
  }
}

In this updated version, a unique identifier (id) is generated for each instance of the UppercaseDirective using a counter (nextId). This ensures that each instance has a unique identifier. The id is then exposed through the controlId getter.

Now, when you apply the appUppercase directive to multiple inputs, each instance will have a unique identifier, preventing the "More than one custom value accessor" error. You can use this identifier in your template or component if needed.