What is Eldritch Blast’s maximum range?

To fulfil a prophecy: What is Eldritch Blast’s maximum range?

Assuming the following constraints:

The allowed material is the PHB, DMG, MM, EE, SCAG, XGtE, VGtM, MToF and the SA Compendium V 2.3 and the therein linked errata.

The setting is the Forgotten Realms, 1492 DR.

The character is level 20 and conforms to PC rules.

The character is allowed to multiclass and may indulge in optional rules.

The character is a Tiefling.

The character has access to up to 5 major magic items and up to 20 minor magic items (XGtE 135), but not to artefacts.

The process has to exclude Wish and Gate whether cast by a magic item or not.

The process has to be reliable (at least 95% of times once during a long rest or more consistently) and reproducible.

The character is without allies at the start of the process but may create or conjure allies. The Tiefling knows no friendly creature.

The whole set-up has to be prepared within 10 rounds, and Eldritch Blast’s has to be cast on the 11th round on the turn of the Tiefling, completing the process.

How can a Sorcerer/Warlock use 4 Eldritch blasts in one round?

How is it possible for the infamous Sorlock multiclass to use 4 x Eldritch blasts in 1 round?

I get the extra damages as in the d6s and +mod damage from all the curses but I see formulas around like 4d10+4d6+64 (aasimar build), then 8d10+8d6+108.

I’m pretty much looking for an explanation or guide of action on how this is possible.