@gamernicki As the guide says, your sim needs to create a forbidden fruit using the Research Station, specifically performing the gene splicing experiment on an existing seed of some kind. (They're easy to find on the ground out in the world.) This is only one possible outcome, but since seeds are plentiful, it's not hard to keep trying.
For the sim that can't go to work, what career are they currently in? If you have room, try placing another rabbithole for that career somewhere in the world, delete the first one (so the sim will automatically work at the new location), and see whether that helps.
For Generations, do you own it through Steam or the EA App? Steam doesn't recognize packs bought through the EA App, although the App does accept Steam CD keys.
Finally, let me know if you use or are willing to add some mods to try to get around the first two issues.