$ apt policy iptables
iptables:
  Installed: 1.8.5-3ubuntu1
  Candidate: 1.8.5-3ubuntu1
  Version table:
 *** 1.8.5-3ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu groovy/main amd64 Packages
        100 /var/lib/dpkg/status
$ iptables -V
iptables v1.8.5 (nf_tables)
$ sudo iptables-save 
$ sudo iptables-restore <<EOF
> *filter
> :INPUT - [0:0]
> COMMIT
> EOF
iptables-restore: line 3 failed
$ 
$ sudo iptables-save 
$ sudo nano /etc/apt/sources.list
$ sudo apt update 
<snip>
$ sudo apt upgrade 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
  apt iptables libapt-pkg6.0 libip4tc2 libip6tc2 libxtables12
6 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
<snip>
$ apt policy iptables
iptables:
  Installed: 1.8.5-3ubuntu2.20.10.1
  Candidate: 1.8.5-3ubuntu2.20.10.1
  Version table:
 *** 1.8.5-3ubuntu2.20.10.1 500
        500 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     1.8.5-3ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu groovy/main amd64 Packages
$ iptables -V
iptables v1.8.5 (nf_tables)
$ sudo iptables-save 
$ sudo iptables-restore <<EOF
> *filter
> :INPUT - [0:0]
> COMMIT
> EOF
$ 
$ sudo iptables-save 
# Generated by iptables-save v1.8.5 on Fri Nov  6 08:43:34 2020
*filter
:INPUT ACCEPT [14:1052]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
COMMIT
# Completed on Fri Nov  6 08:43:34 2020