3d6

I think you have to decide what you mean when you say "support" because in my mind it could encompass everything except damage. But I think a Sorcerer X/ Order Cleric 1 is probably up there. CHA SAD, heavy armor and a shield, CON save proficiency, good level 1 cleric spells, and then you can spend your days twining haste, picking people up with Healing Word then granting them an attack immediately afterwords, careful spelling Hypnotic Pattern, and have your choice of Sorcerer subclass. Divine Soul is the most obvious option but a good argument could be made for Clockwork or Aberrant as well. Because you are CHA SAD you can act as a face, and because you have heavy armor, a shield, and all the low level defense spells, you can act as a frontliner. If you take Warcaster you can use Booming Blade to properly tank a good bit. Or maybe throw in Ritual Caster for Find Familiar so you can act as a scout as well.

Honestly if you take Divine Soul, you can take Spirit Guardians as well and also act as DPS, and Sorcerer gets Fireball obviously so you can deal with almost anything yourself.

It depends on how you define "support" as well as what sort of circumstance you're fighting in. If you're talking about healing, condition removal, and damage itigation the original support class (cleric) can still be extremely effective. Grave and Twilight domains are very good at this, but the "vanilla" Life domain also consistently puts out a bunch of healing while being able to act as a backup tank. Clerics also have the spell versatility to throw out some clutch damage spells at just about any level when not using their support abilities. I used to play in a group with a Life cleric and a Shepherd Druid; between the two there was so much healing that we weren't really ever afraid of going down as long as we didn't really mess up and the cleric's spells and druid's summons could still control the flow of combat and deal their share of damage.