Libssl seems to be a problem, also libc - here the output from CentOS 7:
CentOS 7, which is widely used, comes with glibc 2.17 and openssl 1.0.2k.
Code:
# ldd proxmox-backup-client pxar | grep -e 'not' -e :
proxmox-backup-client: .
/proxmox-backup-client: /lib64/libc.so.6: version `GLIBC_2.25' not found (required by ./proxmox-backup-client)
./proxmox-backup-client: /lib64/libc.so.6: version `GLIBC_2.18' not found (required by ./proxmox-backup-client)
libssl.so.1.1 => not found
libcrypto.so.1.1 => not found
pxar:
./pxar: /lib64/libc.so.6: version `GLIBC_2.18' not found (required by ./pxar)
libssl.so.1.1 => not found
libcrypto.so.1.1 => not found
CentOS 7, which is widely used, comes with glibc 2.17 and openssl 1.0.2k.