Less secure app access is missing because this feature has been removed by Gmail itself.
So, to use Gmail with PHP Mailer so you have to follow the video link or steps shown below:
Video Link: https://youtu.be/syRQ-cYI4Jw
OR
Step 1: Go to Gmail > Manage My Google Account

Step 2: Go to “Security”

Step 3: Turn on “2-step verification”

Step 4: After that click on “App Password” below the 2-step verification
You will be asked to enter your Gmail password!

Step 5: Click on the “Select App” dropdown and choose the “Other” option

Step 6: You will be asked to write the name of your app (write any name)

Step 7: A popup will open and you will get a generate key from Gmail (Copy it!).

Step 8: Paste the copied key in your password field in PHPMailer.

All done!