Fread(): file created in the system's temporary directory at /var/www/nextcloud/apps/files_external/3rdparty/icewind/streams/src/Wrapper.php#91

ℹ️ Support
,
4

Might check value of sys_temp_dir
in
/etc/php/7.3/fpm/php.ini

see “HEADERS on invalid stream”
and this post on seemingly similar issue