All, like others I too am on a Synology using the built in Let’s Encrypt support. I am on DSM 6.2.1-23824 Update 4.
I received the email about TLS-SNI-01 deprecation. I’m very sure that I am only using LE with the Synology at this point and definitely in the last 60 days.
But, I see some other threads that the Synology doesn’t use that method, so why the email if true?
Interestingly, we make use of a Synology at work with LE certs and have not (yet) received an email about this.