Pokemon Radical Red

Radical Red is a QoL hack that has many new features, such as:

Physical/Special split + Fairy Typing
All Pokémon up to Gen 8 obtainable (with some exceptions, see further down)
Moves up to Gen 8, including some of the Isle of Armor DLC moves!
Updated Pokémon sprites
Mega Evolution
Abilities up to Gen 8
Important battle items up to Gen 8
Raised level cap to 250, although this won't be super relevant until post game is added
Raid Battles
Reusable TMs
Expanded TM list
Additional move tutors
EV Training Gear
Ability popups during battle
Gen 8 Exp Share
Hidden Abilities
Day and Night
DexNav, which allows you to search for Pokemon with hidden abilities and other neat things!
Even faster turbo speed (!!!)
Abilities like Magma Armor have field effects like recent Gens
Destiny Knot, Everstone have updated breeding mechanics
... and more!