The server must return the same file to the nested path. How to do?

Question

htaccess

Good evening!
Helped with a question about using Vue router in a nested route
However, I did not understand (I do not know how to do) the phrase:

the server, in turn, should always return index.html to :/dash/vue/**/*

So far, this is the situation - I go to the dash / vue / folder, which contains index.html and calmly walk along the routes, but when I refresh the page, a redirect to 404 is triggered.
What should I do?
In the root .htaccess I have this:

ErrorDocument 404 /404.php

RewriteEngine Off
RewriteCond %{SERVER_PORT} !^443$
RewriteCond %{REQUEST_URI} !^/[0-9]+\..+\.cpaneldcv$
RewriteCond %{REQUEST_URI} !^/\.well-known/pki-validation/[A-F0-9]{32}\.txt(?:\ Comodo\ DCV)?$
RewriteRule .* https://%{SERVER_NAME}%{REQUEST_URI} [R=301,L]

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^.]+)$ $1.php [NC,L]
RewriteRule ^article/([a-zA-Z0-9_]+)/? article.php?index=$1 [QSA,L]