Newly upgraded to EE6, now we cannot access our members' SIGNATURE fields?

Any guidance here would be much appreciated.

We recently upgraded our site from a very old version of EE to the new EE6. In the old site, we used the members’ SIGNATURE field (which showed in the member panel) to store a particular type of data for our members. But after upgrading to EE6, we noticed that although the SIGNATURE field is still in the database and shows on the site, there is nowhere to access the content via the control panel?