Baikal DAV

http://sabre.io/baikal/install/

wget https://github.com/sabre-io/Baikal/releases/download/0.6.0/baikal-0.6.0.zip
unzip baikal-0.6.0.zip
mv baikal /var/www/html
cd /var/www/html
chown -fR www-data:www-data baikal
apt-get install nginx php7.3 php7.3-sqlite php-sabre-dav

NginX vhost:

server {
  listen       80;
  server_name  default_server;

  root  /var/www/html/baikal;
  index index.php;

  rewrite ^/.well-known/caldav /dav.php redirect;
  rewrite ^/.well-known/carddav /dav.php redirect;

  charset utf-8;

  location ~ /(\.ht|Core|Specific) {
    deny all;
    return 404;
  }

  location ~ ^(.+\.php)(.*)$ {
    try_files $fastcgi_script_name =404;
    include        /etc/nginx/fastcgi_params;
    fastcgi_split_path_info  ^(.+\.php)(.*)$;
    fastcgi_pass   unix:/var/run/php/php7.3-fpm.sock;
    fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
    fastcgi_param  PATH_INFO        $fastcgi_path_info;
  }
}

Nginx proxy with configured upstream:

server {
  listen 80;
  server_name baikal.server.tld;
  return 301 https://$host$request_uri;
}

server {
  listen 443 ssl http2;
  server_name baikal.server.tld;
  root /var/www/html;
  index index.php index.html index.htm;
  location / {
    gzip off;
    proxy_read_timeout 300;
    proxy_connect_timeout 300;
    proxy_redirect off;
    proxy_set_header Host $http_host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto https;
    proxy_set_header X-Frame-Options SAMEORIGIN;
    proxy_pass http://caldav;
  }
  ssl_certificate /etc/letsencrypt/live/cert.tld/fullchain.pem;
  ssl_certificate_key /etc/letsencrypt/live/cert.tld/privkey.pem;
  include /etc/letsencrypt/options-ssl-nginx.conf;
  if ($scheme != "https") {
    return 301 https://$host$request_uri;
  }
}

Go to setup wizard and select SQLite db while installing it. Configure user and calendar. Calendar is then available via DAV at baikal.server.tld/html/cal.php/calendars/ via browser.