It’s September 30 and the old Let’s Encrypt root certificate expires, so check your sites

[George]

Normally everything should be all fine as the new Let’s Encrypt root certificate is already well known to all the new browser and servers.

But still if you run an old server, you might want to check if all root certificates are well updated.

See:

DST Root CA X3 Expiration (September 2021) - Let's Encrypt