This R3 is expired (and has been retired for a long time now):
https://letsencrypt.org/certs/lets-encrypt-r3-cross-signed.pem
This R3 is current:
https://letsencrypt.org/certs/lets-encrypt-r3.pem
If you want to use the "long chain", use that last R3 PEM file I provided along with this one:
https://letsencrypt.org/certs/isrg-root-x1-cross-signed.pem
Only using the R3 intermediate certificate without using the ISRG Root X1 intermediate certificate is known as using the "short chain".
Personally, I use the "short chain" with my GoDaddy cPanel shared hosting because it avoids some headaches in cPanel that using the "long chain" can cause, particularly with the mail subdomain.