NgxMatDatetimePicker is not assignable to type MatDatepickerBase
in this case you have to disable strict template checking explicitly, you can make use of the $any() template function:
<input matInput [ngxMatDatetimePicker]="picker" placeholder="Choose a date" formControlName="scheduledStartDateTime" [min]="minDate" (dateChange)="dateUpdated()" ><mat-datepicker-toggle matSuffix [for]="$any(picker)"></mat-datepicker-toggle><ngx-mat-datetime-picker #picker [showSpinners]="true" [showSeconds]="false" [stepHour]="1" [stepMinute]="1" [stepSecond]="1" [touchUi]="false" [enableMeridian]="false" [disableMinute]="false" [hideTime]="false"></ngx-mat-datetime-picker>