Do I need to go to Immigration for an ED visa extension due to the amnesty until July 31?

This amnesty is not for long-term visa holders. If you want to lose your visa don't go and renew it at immigration.

Retirement, education, volunteer, business 3 month or one year process as normal.

Or you could listen to the experts leaving Thailand July 31st because they didn't extend their visas because they thought they were the same as tourists and visa exempt travellers.

You don't have to do anything, but remember that you will have to leave Thailand before 31 July if you don't extend your permission to stay. If the borders don't open before 31 July, the amnesty may be extended but there is no guarantee of this. Personally, I would go to Immigration and do your extension if you can, assuming you plan on continuing to study here. Immigration after 31 July will be a scrum!

No, anything that expires before July 31st is automatically extended to July 31st. No need to go to immigration.