Need to keep application links confined to subdirectory

First: This is NOT the standard “how to run or install WordPress in a sub-directory”

I have a self-hosted Wordpres site. WordPress is intalled at the root directory for my website hosting folder.

Now I am doing something I have done many times. Putting a separate non-WP application in a sub-directory folder. This application refers to a different MySQL database than the WP install database.

The path to this application folder looks like this —

myWordPress-website (WP files) /nonWPapplication folder

the url shows up like this —

https://mywordpress.com/mynonWPapp/index.php
https://mywordpress.com/mynonWPapp/login.php
https://mywordpress.com/mynonWPapp/logged-in-formpage.php
https://mywordpress.com/mynonWPapp/signout.php

There may be other pages added in the /mynonWPapp folder.

There are a lot of internal file links in this application to stylesheets, images, js files, functions, actions, CRUD pages to edit the database installed for this app.

I’m having a problem keeping all the links inside this folder from mistakenly looking for a file or resource back in the base WordPress installation at https://mywordpress.com

I know I can install permissions and re-writes in the new application folder but I want a clean one-stop rewrite solution at the base of my wordpress site. Also hand users looking for this application with a misspelled page url, for instance.

Incorparating rewrite rules into my base WordPress .htaccess file that also keep all links inside the subdirector folder /mynonWPapp/ sorted is where I need help. I don’t want to swamp my server with unnecessary Redirect & Rewrite rules, too.

Is this a situation some of you have already solved with .htaccess rules?

Thank you for your kind responses.