Foreign Key dropdown is missing when editing a column in a row, now a simple textbox shows #2567

Description

I have a table with a Foreign Key in a column.
A long time ago, Heidi was enhanced to show a dropdown when I edit a row in the main table, so I can select the appropriate value from it.
Now the dropdown has disappeared, all that is left is a textbox where I can manually enter some text.
Please restore the dropdown-functionality.

HeidiSQL version and OS

Windows 12.20.0.7320

Database server version

MSSQL 16.0.4165 RTM on Ubuntu 20

Reproduction recipe

Error/Backtrace