You should be able to achieve this if the system parameter “Self-Service Form Two Column Layout System Parameter” is set to true. This way the layout of forms (all) in the Self-Service portal is a two column layout. You then set the field’s Size in the customiser as
Narrow and Normal » displayed half the width of a row.
Thank you @Caroline Schaffner. Although we are upgrading to that version in the coming months, I forgot to mention we are currently using v 11.5. I didn’t see that option in System Parameters in the version we are using. Any idea how to do it with our current version?