You can allow users to update their records directly with the miniExtensions form without needing to log in or creating an account anywhere!
The form can generate a unique editing URL for every record in your table. You could then email this link to your users so they can access their record. You have full control over which fields are shown and which fields are editable by the user.
To set this up, do the following:
Click Share Form
Select Form for Editing Records.
A modal will show up. You can copy the text from formula box using the Copy button. You can also test this feature by clicking the Try it out button. This will open the editing form in a new tab with a record from your table.
Lastly, create a new formula (or button) field in Airtable and paste in the formula you just copied. This will now generate a unique link for each record that you could send to your users, for example via email using an Airtable automation!
The editing formula option is not accessible if you have the login feature enabled. Once disabled, you'll be able to see it.
Prefill
In most cases, it doesn't make sense to prefill a form if you're updating an existing record. Prefilling mostly makes sense when creating a new record. When editing a record, the form will be prefilled with the record's existing data automatically. Prefilling dynamic values is possible by using a formula in Airtable to add the prefill parameters. This part has to be done in Airtable, not in miniExtensions.
Login Page
If you have recurring users who need to update their data repeatedly, then a login screen might be a better fit. But if your form users are one-off customers, then the login screen might not be needed.