When you’re using Apache put this at the bottom of your .htaccess file:
<IfModule mod_rewrite.c>
Options -MultiViews
RewriteRule ^core/js/oc.js$ index.php [PT,E=PATH_INFO:$1]
RewriteRule ^core/preview.png$ index.php [PT,E=PATH_INFO:$1]
RewriteCond %{REQUEST_FILENAME} !\.(css|js|svg|gif|png|html|ttf|woff2?|ico|jpg|jpeg|map|webm|mp4)$
RewriteCond %{REQUEST_FILENAME} !core/img/favicon.ico$
RewriteCond %{REQUEST_FILENAME} !core/img/manifest.json$
RewriteCond %{REQUEST_FILENAME} !/remote.php
RewriteCond %{REQUEST_FILENAME} !/public.php
RewriteCond %{REQUEST_FILENAME} !/cron.php
RewriteCond %{REQUEST_FILENAME} !/core/ajax/update.php
RewriteCond %{REQUEST_FILENAME} !/status.php
RewriteCond %{REQUEST_FILENAME} !/ocs/v1.php
RewriteCond %{REQUEST_FILENAME} !/ocs/v2.php
RewriteCond %{REQUEST_FILENAME} !/robots.txt
RewriteCond %{REQUEST_FILENAME} !/updater/
RewriteCond %{REQUEST_FILENAME} !/ocs-provider/
RewriteCond %{REQUEST_FILENAME} !/ocm-provider/
RewriteCond %{REQUEST_URI} !^/\.well-known/(acme-challenge|pki-validation)/.*
RewriteRule . index.php [PT,E=PATH_INFO:$1]
RewriteBase /
<IfModule mod_env.c>
SetEnv front_controller_active true
<IfModule mod_dir.c>
DirectorySlash off
</IfModule>
</IfModule>
</IfModule>
Or follow the documentation and alter your .htaccess automatically with the occ command described here:
https://docs.nextcloud.com/server/18/admin_manual/installation/source_installation.html#pretty-urls