I'm just wondering at what lvl I should grind for to beat the elite four cuz I'm having a hard time

lvl 100

I literally just beat the elite 4 and trained 4 of my Pokémon to level 90 to do it. I tried it with 4 of them at 80 and 2 at 70, but I couldn’t get past Lance’s Dragonite at that level since I didn’t have any ice, dragon, or fairy type moves to fight it with. Now that I’m moving on to other regions I hope gyms are still a challenge even given how high level my Pokémon are.

I have used a team of lv.80 random natures, evs n low ivs...team consisted of Charizard, Gyarados, Raichu, Alakazam, Dewgong n Gengar...

Defeat E4 in first attempt with that combination....

prioritize setup pokes, a lvl 80 gyarados with dragon dance can do more work than a lvl 100 trash without setup moves

i advice you to get gyarados and scizor in your team

gyarados: dragon dance waterfall earthquake ice fang

scizor with technician ability: sword dance bullet punch roost

gyarados is one of the most common pokes and scyther is catchable lvl 65-70 in pinkan island, you can't go there but people that can go there can sell you one freshly caught for cheap