Hi Anamaria. I was able to contact my hosting provider siteground and they were able to tell me what was causing the 403 error that was hindering the theme panel to be updated. It was blog-vault backup. I did not see the plugin in the dashboard, but it was in file manager.

I renamed it to “blog-vault-backup-old” to disable it and it worked!
It is now updating properly.
I hope this information helps anyone else having the same problem
https://imgbb.com/vxxwR4g

• This reply was modified 4 years by akarim.

Thanks for your response Anamaria.
have a great day