Per below that hasn't been determined yet. Are you aware though that there are two paths through the intermediate chain provided by Let's Encrypt? Most modern clients (and probably all modern browsers) will use the chain leading to ISRG Root X1. The intermediate chain path to DST Root CA X3 is provided for compatibility to old Android clients. Let us know if you want more details on these two paths. Hard to tell your level of expertise from the question.
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