I have no quick answer but here are some ideas and information.
Here is what the manual has to say about depreciated modules.
modules: deprecated: This contains a list of deprecated modules. This is the only way to access deprecated modules for new edits but be warned: these modules will be removed for new edits in the next release of darktable. This group cannot be duplicated and the modules within it cannot be added to user-created groups.
When I open this is the list I get, but I have upgraded frequently (Fedora) and did not go strait from 2.6.
Global Tone Map
Do you have the option to test debian 11 and dt using a bootable usb drive? Do you have a recovery plan if you need to revert? Make sure you backup the data base before you upgrade or test as the database will be updated.