I'm for: only flag a forbidden term when the source segment contains the relevant source term. 

Otherwise, why on earth does the Status (System) contain this status of Forbidden on a language-specific term level? If it does NOT check the source term first, why not simply form a standalone black list for all forbidden terms to avoid them from being used entirely anywhere in the document? 

This has worked in memoQ for years.

It's a simple, single check box and the deprecation handling works exactly as expected.

So you can have

- a blacklist, e.g. if you are translating a marketing text and want no old product names in there at all

- or a deprecated-per-term setup, where you have new terms for some things but these are not global

There's simply zero excuse for it to not work in Studio.

I have a client who has painstakingly set up a large Trados termbase for this and we, as translators, now regularly generate F8 reports with thousands upon thousands of errors, of which about 99.5% are false alarms. Utterly useless.

Agree, cf. https://community.rws.com/product-groups/trados-portfolio/trados-studio/f/studio/40562/quality-check-terminology-forbidden-picklist-fields-any-way-to-have-this-trigger-depending-on-source-terms for another take on why this should really be fixed.

Definitely agree. A target term that's defined as a "forbidden" translation of a particular source term is not necessarily forbidden everywhere!
I can sort of understand why the tool is built this way (if a term really is forbidden, then you don't want it anywhere in your document), so perhaps there needs to be some kind of setting to determine which behaviour the user wants: always flag forbidden terms, or only flag them when the source segment contains the relevant term.