Stopping record form from submitting

Question

I created datatable with onrowselection and after selecting a row the details will pass to a record form for editing. Now I want to prevent the record form from submitting in a certain condition. I tried event.stopPropagation() and event.preventDefault() but it doesn't work or I used them incorrectly. Does anyone know a way for this to happen? I appreciate any help.

HTML:

<template if:true={showModel}>
            <lightning-tab label="Car Model" onactive={handleModelData}>
                <lightning-input placeholder="Search Model" onkeyup={handleModelKeys}>
                </lightning-input><br/>  

                <div style="height: 15rem;">
                    <lightning-datatable key-field="id" data={modelRecords} columns={CarModelColumns} 
                        onrowselection={getSelectedModel}>
                    </lightning-datatable><br>
                </div><br>
                <lightning-tabset variant="scope">
                    <template if:true={showCarModelForm}>
                        <lightning-tab label="Create">
                            <lightning-record-form object-api-name="Car_Model__c" 
                                columns="2" layout-type="Full">
                            </lightning-record-form>
                        </lightning-tab>
                    </template>
                    <template if:true={showCarEditModelForm}>
                        <lightning-tab label="Edit">
                            <lightning-record-form object-api-name="Car_Model__c" 
                                columns="2" layout-type="Full" record-id={recordModelId} onsubmit={handleSubmit}>
                            </lightning-record-form>
                        </lightning-tab>
                    </template>
                </lightning-tabset>           
                
            </lightning-tab>
        </template>

JS:

recordModelId;
    getRow = [];
    getSelectedModel(event) {
        const selectedRows = event.detail.selectedRows;
        this.getRow = selectedRows;
        this.recordModelId = selectedRows[0].Id;
        this.showCarEditModelForm = true; 
        alert('Record: ' + this.getRow[0].Id + ' ' + this.getRow[0].Safety + ' ' + this.getRow[0].Quality);
        
    }
    handleSubmit(event){
        User().then(curUser => {
            if(curUser == 'Factory' && this.getRow[0].Stage != 'New'){
                event.stopPropagation();
                event.preventDefault();
                alert(this.getRow[0].Model + ' is currently/passed Manufactured Stage');
            } else {
                this.recordModelId = this.getRow[0].Id;
                this.showCarEditModelForm = true; 
            }
            if(curUser == 'Quality Analysts' && this.getRow[0].Safety == false && this.getRow[0].Quality == false){
                event.stopPropagation();
                event.preventDefault();
                alert(this.getRow[0].Model + ' Safety and Quality hasn\'t passed yet!');
            } else {                
                this.recordModelId = this.getRow[0].Id;
                this.showCarEditModelForm = true; 
            }
        })
    }