As a Note, Longswords are Versatile and even list the one-handed and two-handed properties but players can't pick which one. It defaults to two-handed unless a shield is equipped leaving it impossible to dual wield.
Bit of a pedantry note, but the pen & paper rules as written do require both weapons involved in 'two-weapon fighting' to have the "Light" property tag, which the longsword doesn't have. Shortsword, scimitars, etc., yes. So that is actually accurate, unfortunately. (p. 195 in the PHB, if you'd like a citation) The only way to get around that is the Dual Wielder feat, which idk if they've implemented?
Depending on your interpretation of the Dueling fighting style (and whether it can be used with a shield in the off-hand or it's meant to be Errol Flynn-style sword and flourishy bare hand), it could very much nerf using a longsword with that fighting style, though. So there is still a case for allowing one-handed wielding without a shield, I'm just not sure how you'd flag it so you can't dual-wield unless you had the feat, assuming they put that in.
(Separate argument over sticking to RAW vs. common house rules/QoL changes not pictured, though I'm sure it's ongoing in other places on the forums)
