Hey! Unfortunately I don't have access to my laptop for a day or two. But the general rule of thumb to get on Izumi's route is to not give too much attention to Souma while supporting Izumi whenever it comes up.
Below is a guide I wrote long ago for Souma's route. Avoid these options as much as possible. If you still can't get on Izumi's route let me know! I can type up a guide by Thursday, give or take.
Sorry the solution is so long winded 😅😅
[[[spoilers CLEARLY ]]
1. What brings you here?
2. It's okay, I'll hear him out.
3. Run Away.
4. Serve him yourself
5. Chase After him.
6. Invite him over to share Gram's dinner
7. Wish for Souma to be nice to you.
8. Invite him in/Get him a drink
9. Don't interfere
10 . Boop the snoot/Misdirect
11. Tell her about Souma
12. Take a quick Nap