Would I be correct if I rule that a character with a spear/javelin or other throwable weapon in hand an the beginning if their turn can do two ranged attacks as part of the extra attack feature? But if the character had another weapon in their hand (a sword) and wanted to throw a javelin they would only be able to attack once, even though they had the extra attack feature (drop sword on ground - draw throwable - throw weapon). To draw another throwable would cost an action and they don’t have one to spend at this time.

Correct.

"You can also interact with one object or feature of the environment for free, during either your move or your action. For example, you could open a door during your move as you stride toward a foe, or you could draw your weapon as part of the same action you use to attack.

If you want to interact with a second object, you need to use your action. Some magic items and other special objects always require an action to use, as stated in their descriptions."

There is one exception, if the player has the thrown weapon fighting style they draw the thrown weapon as part of their attack. Fighters with this style could theoretically drop sword, throw 2-4 javelins depending on level, then use their object interaction to pick the sword back up.

In the game I DM and in one that I play in we allow characters to ready or stow a weapon or potion as a Bonus Action but that's a house rule.

Quote from bjornsundell >>

Would I be correct if I rule that a character with a spear/javelin or other throwable weapon in hand an the beginning if their turn can do two ranged attacks as part of the extra attack feature? But if the character had another weapon in their hand (a sword) and wanted to throw a javelin they would only be able to attack once, even though they had the extra attack feature (drop sword on ground - draw throwable - throw weapon). To draw another throwable would cost an action and they don’t have one to spend at this time.

 Sounds like something that should definitely be house ruled to allow throwable weapons to work.

It's what the Thrown Weapon Fighting Style is for. Otherwise - it's one if they used their free item interaction to draw the first javelin - or two if they already had a javelin drawn before the start of their turn. They could draw and throw a third if they use their Action Surge to do the second item interaction - but that's about the limit without the Fighting Style.

Quote from bjornsundell >>

Would I be correct if I rule that a character with a spear/javelin or other throwable weapon in hand an the beginning if their turn can do two ranged attacks as part of the extra attack feature? But if the character had another weapon in their hand (a sword) and wanted to throw a javelin they would only be able to attack once, even though they had the extra attack feature (drop sword on ground - draw throwable - throw weapon). To draw another throwable would cost an action and they don’t have one to spend at this time.

 Correct. But you could also throw both the javelin and the sword as an improvised weapon with Extra Attack though.

Improvised Weapon: If a character uses a ranged weapon to make a melee attack, or throws a melee weapon that does not have the thrown property, it also deals 1d4 damage. An improvised thrown weapon has a normal range of 20 feet and a long range of 60 feet.

5e is really unforgiving when it comes to a thrown weapon concept, despite it being a classic trope in fantasy with popular examples like Thor's Mjolnir or Wulfgar's Aegis-fang. Personally I amend all magic weapons with the thrown keyword to immediately return to the wielder's hand similar to how the Artificer's Returning Weapon infusion works.

Quote from scatterbraind >>

5e is really unforgiving when it comes to a thrown weapon concept

I agree.

In my games, I houseruled that if you have some way to get at the thrown weapon really quickly, then you can use Extra Attack or Multiattack.

For example, sticking your javelins in the ground in front of you, or having darts in a bandolier, or having a spearcarrier hand you spears, or starting the combat with several darts already palmed.

Considering that ammunitions can freely benefit from being able to overcome the 1 free object interaction per turn when attacking, it's not unbalancing to allow thrown weapons to also have such benefit.

TBH the sentence "you can draw a weapon that has the thrown property as part of the attack you make with the weapon." should have been an errata to the Thrown property rather than a feature in a fighting technique.