I think this question is important. Kind of feels this is a re-occuring problem with missing best practise advise.
Both links mentioned above are dead, so I add my use case as an example why this might be necessary:

• Backend Class to extend Link Handler with possibility to link to a specific record (detail page).

• The record is no extbase-record, though, but fetched from external. So technically spoken I need just a link to a specific detail page, adding one or multiple parameters. Only that the uid of this detail page can not be hard-coded.

• The package is technically demanding and re-usable. The mentioned detail page for a specific Installation now is defined by editors using TypoScript constants. The setting is used on multiple occasions (FE plugins) - not only for the link handler. There are other settings also.

• I do not see a reasonable possibility for the editor to set the same setting by TSConfig (apart from the fact that this kind of redundancy would be unclean and error-prone). Basically, this constant should be enough for all use cases, so also for the link handler. For TYPO3 12 it works just that way.

• Although I think it's good to have all the settings in one place for ease of use, I'm generally open to another solution if necessary. I need advise and expertise, though. It seems a problem touched by future strategy maybe.

Cut short: I need also access to TypoScript from Backend Class, outside of Extbase Controller. Working for Typo3 12 using TYPO3\CMS\Core\TypoScript\TemplateService or BackendConfigurationManager as mentioned above. No working version for Typo3 13.

Thanks for any hint!