Can I disable the auto redirect of http to https?

Just use a clear HTTP address as the site address:

http://example.com {
    reverse_proxy ....
}

Automatic HTTPS is enabled if your site’s address contains a hostname or IP address. This behavior is purely implicit, however, so it never overrides any explicit configuration. For example, if the site’s address is http://example.com , auto-HTTPS will not activate because the scheme is explicitly http://

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