Cannot get RC (Apache, snap) working in subfolder

Description

I have a fairly standard LAMPs server running on a bananapi (Armbian). With a Let’s Encrypt certificate obtained with a cerbot-script.
I also installed RC with snap, and I can see it running on port 3000, log into it, etc.
No problems so far.

Then I want it to run in a subfolder and followed instructions on
https://rocket.chat/docs/installation/manual-installation/running-in-a-sub-folder/

But all I get is a blank page. Awkwardly, if I look at the source of the blank page, I can see the html-code of RC!

Have a look at https://noppesict.nl/chat (temporary experimental server)

Server Setup Information

I also tried

sudo snap set rocketchat-server site-url=https://noppesict.nl/chat
sudo snap set rocketchat-server root-url="https://noppesict.nl/chat node main.js"
sudo systemctl restart snap.rocketchat-server.rocketchat-server.service
sudo snap set rocketchat-server caddy=disable   # I do not need caddy

sudo snap get rocketchat-server

result:

Key              Value
caddy            disable
https            disable
mongo-oplog-url  mongodb://localhost:27017/local
mongo-url        mongodb://localhost:27017/parties
port             3000
root-url         https://noppesict.nl/chat node main.js
site-url         https://noppesict.nl/chat

This is my 000-default-le-ssl.conf

<IfModule mod_ssl.c>
<VirtualHost *:443>
	ServerAdmin webmaster@localhost
	DocumentRoot /var/www/html
	ErrorLog ${APACHE_LOG_DIR}/error.log
	CustomLog ${APACHE_LOG_DIR}/access.log combined
ServerName noppesict.nl
SSLCertificateFile /etc/letsencrypt/live/noppesict.nl/cert.pem
SSLCertificateKeyFile /etc/letsencrypt/live/noppesict.nl/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
SSLCertificateChainFile /etc/letsencrypt/live/noppesict.nl/chain.pem
<Location /chat>
    Require all granted
    RewriteEngine On
    RewriteCond %{HTTP:Upgrade} =websocket [NC]
    RewriteRule /var/www/html/(.*)           ws://localhost:3000/$1 [P,L]
    RewriteCond %{HTTP:Upgrade} !=websocket [NC]
    RewriteRule /var/www/html/(.*)           http://localhost:3000/$1 [P,L]
    ProxyPassReverse http://localhost:3000
</Location>
</VirtualHost>
</IfModule>

What can I do to make RC run under the /chat subfolder? Or, what am I doing wrong?
PS: Running in a subdomain, like chat.noppesict.nl is no option.

Looks like I am not th only one with this problem: https://stackoverflow.com/questions/…