I don't host with ionos but looks like their script to install a moodle takes what they think is an extra protection (or a work-around) with this:
see the dot in front of that directory name?
Typical standalone servers use /var/www/ as home directory for apache user and one can create (manually) a moodledata folder there ... apache user/group can see/use.
Typical (many) hosted servers use public_html and user is kinda in a jail. May not be able to put moodledata outside of public_html and have moodle see it in /home/accountname/ or something like that.
What's in .htgcld34ieljdj.data?
And what's in: .htxt8cvv.appconfig.php
If one were hosted where one is on a VPS (dedicated just to one customer), one could easily install the php xmlrpx extension via package manager .. CentOS 6 or 7 that's yum ... Debian/Ubuntu that's apt-get.
Do you have something like 'EasyApache'? ... which allows choosing PHP version but also which extensions are loading?
If you put a phpinfo.php page at code root and access it directly one should see which php.ini file is being used and in some cases how PHP was compiled.
Slasharguments is really 'AcceptPathInfo' in apache 2.4.
where it says can be configured in .htaccess
Now if it can't with your hosting, contact hosting helpdesk.
All I can say is good luck!