I don’t know, there are 730,000 highway=footway with bicycle=yes and 85,000 with designated. Many of them look like separately mapped shared use pavements/sidewalks, or pavements with cycle paths (“tracks”) on them. If that’s troll tagging then we have an even bigger problem.
I’ve just spot checked a few highway=footway with oneway=yes with the help of Overpass. Judging from the map, many of them look like shared use pavements or pavements with cycles paths on them, where the oneway tag was used to say that cycling is only allowed in one direction. Many others are in amusement parks, train stations etc. and presumably are true one-way footpaths.
There may be some country-specific differences: the examples I saw in the US when checking with Overpass are nearly all true pedestrian one-ways, the ones in Europe seem to be mostly separately mapped pavements where the oneway tag was meant for bicycles. Not sure why!
In fact StreetComplete is planning to add a quest asking users in Germany to check, for a highway=footway (or path or cycleway) with bicycle=designated if the path is one way for bicycles or not. The plan is to add oneway=yes or no to such ways to express this. There’s even a MapRoulette challenge to systematically replace existing oneway:bicycle with oneway on such paths. This is of course all based on an assumption that there is community consensus that oneway should only apply to vehicles (including bicycles)… if you object to that you might want to comment on the Github issue!
I think we can all agree that oneway=yes or oneway=no can never apply to someone who is not allowed to use the path, and that access tagging should be used to indicate who is allowed to use it.