Попробуйте это: [attr.disabled]="true"
<select name="modulo" id="modulo" class="form-control modulo" formControlName="id_modulo" [attr.disabled]="true">
<option value="{{ m.id_modulo }}" *ngFor="let m of modulos" >{{m.nome_modulo }}</option>
</select>
FormBuilder в компоненте:
this.formulariosForm = this.formBuilder.group({
id_formulario: [null],
nome_formulario: [null, Validators.required],
descricao: [null, Validators.required],
id_modulo: [null, Validators.required],
analista_responsavel: [null, Validators.required],
url: [null, Validators.required]
});