I am currently with H-1B visa but I transferred from OPT so I cannot come back to the US until I have renewed the visa in a U.S Embassy.
Currently, the U.S Embassy in my home country is closed due to COVID-19 and I was wondering if I can renew it from another U.S Embassy in another country or if I can renew it in the U.S, which would be better.
You can't renew it inside the US, but (assuming you haven't violated the terms of a US visa in the past) you can renew it at a US consulate in another country.
If you are currently inside the US, you are not required to have a valid visa in your passport. You only need it, as you note, the next time you plan to enter the US. Accordingly, if you don't plan to leave the US before the end of your OPT, you don't need to renew it at all. If you do need to leave the US, you should make sure that your trip includes an opportunity to renew the visa at a convenient US consulate.
