I have to face one problem on windows 7 safari browser.
When i export pdf file , japanese character of file name is not shown.
Based on your description, it doesn’t sound like this is related to Let’s Encrypt or TLS/SSL at all. You’d probably be better off asking this question somewhere else (maybe Apple’s support community), as it would be off-topic for this site.
Let me know if I misunderstood something about your question.