Show me the rule.

"Different attacks, damaging spells, and other harmful effects deal different types of damage. Damage types have no rules of their own, but other rules, such as damage resistance, rely on the types."
https://www.dndbeyond.com/sources/d...lNrWCeYN253OusM6XDGxQZJs1hyy#DamageTypesNope ... Force is Force, that is why its called Force ... duh. :-/
What are you even talking about here?

When damage is not better described by either a physical or elemental source, it is instead Force damage.
Of all the damage types that exist in the universe, "Force" is the "This doesn't have an actual type" damage type.
There is no "Untyped" or "Unresistable" damage.
where unspecified damage type means its type is based off what caused it
Aaaaand nope.
Again, show me the rule ...
"Hunter's mark uses the same damage type as the attack that triggers it. If the attack has more than one damage type, choose one."
https://x.com/JeremyECrawford/status/808824943299264512"Sneak Attack causes the weapon it uses to deal more damage. The intent is that an unusual weapon like the net that deals no damage doesn't magically start dealing damage with Sneak Attack. But a DM is free to override that intent. The RAW certainly isn't entirely clear here."
https://x.com/JeremyECrawford/status/956930977795735552@Plaguescarred About Warding Bond spell if target and cleric has resistance, is damage halved twice or only once? Resistance is applied only once to any instance of damage. See the Player's Handbook, page 197.
@JeremyECrawford If the cleric has resistance, nothing in the rules says it doesn't work.
https://www.sageadvice.eu/warding-bond/This damage will then follow the standard damage rules and be modified by all damage modifiers on the target
Nope ...
1) The tooltip says clearly "you take the same amount of damage" ... applying mitigations and modifiers would mean X =/= Y ... it is that simple.
2) The PH Page 197 also states "
Multiple instances of resistance or vulnerability that affect the same damage type count as only one instance." >> By applying second resistance, you would broke this rule.
As mentioned by the actual Lead Rules Designer, Warding Bond is 2 instances of damage.
There's the initial damage to the target of the bond. Then a second, separate instance of damage that occurs on the Cleric.
If we go by the basic Damage Rolls guide:
"Each weapon, spell, and harmful monster ability specifies the damage it deals. You roll the damage die or dice, add any modifiers, and apply the damage to your target. Magic weapons, special abilities, and other factors can grant a bonus to damage."
https://www.dndbeyond.com/sources/d...lNrWCeYN253OusM6XDGxQZJs1hyy#DamageRollsThe "Damage Roll" itself is being determined by the damage taken by the target of Warding Bond rather than a dice roll. But then the second part of damage is adding in the modifiers.
This includes changing damage type to being Magical because it is coming from the Warding Bond spell.
https://www.sageadvice.eu/magic-resistance-against-physical-damage/This is why I refer to the Cleric "Double Dipping" in quotes, because it's not actually double dipping. It is only applying its mitigation against a singular source of damage once. It just happens that that source of damage is determined by the damage taken by another target whom themselves can mitigate that damage with their own mitigations.
This is not one singular instance of damage being mitigated twice, but 2 separate instances of damage being mitigated once. Since again, this isn't the attack hitting both the target and the Cleric, this isn't damage becoming "Untyped", this isn't some new mechanic like the Cleric suffering "Health Loss" instead of taking damage. This is Target A takes damage. The damage they receive (After mitigations) is then turned into a new instance of damage on Target B.