My two cents is that multiclassing should be driven first and foremost by what seems cool or fun, then looking at story consideration, and finally looking at optimization. Rogue is one of the best classes for MC, it has endless synergy with basically every other class, so I don't think there is a wrong answer in terms of viability. Rogue/bard is super fun, allowing for a super versatile character in terms of being the face and skillmonkey, rogue/fighter is a potent martial combination, and warlock rogue has neat RP potential and some nice interplay between invocations and roguish abilities (darkness, mask of many faces, etc.)
How has you character been played so far? A dashing trickster would lend itself to bard (swords, whisper, or lore), a deadly and efficient assasssin would lend itself to fighter (BM or echo knight if allowed), or a curious seeker of secrets would lend itself to warlock (hex blade is the best choice for a mixed martial imo).