I am not convinced that the foot=no tag which you added to Highdown Rise in 2022 represents a real and explicitly signed prohibition either. That would make both Highdown Gardens and The Highdown unreachable on foot from Littlehampton Road. It would also make the pedestrian crossing over both carriageways of Littlehampton Road at the end of Highdown Rise a little pointless.

Adding non-existent restrictions in order to influence a single consumer of OSM data is likely to have adverse effects on other data consumers.
https://wiki.openstreetmap.org/wiki/Tagging_for_the_router

If I were determined to tick off Titnore Lane in CityStrides, I would probably wait for a Sunday morning in May-July and go out very early. I also use CityStrides and I do appreciate how frustrating it can be to have streets which are difficult to complete.