Am I using encryption for fix downloads?

SNDPTFORD is the primary concern.
Customers that use SNDPTFORD may be affected, depending on their version of IBM i, and their fix level. This is because SNDPTFORD relies on a driver called the ECC Common Client to download fixes from IBM. The newer versions of this driver support high speed downloads using port 433, and PTFs have been created to provide this support for different releases of IBM i. This change is explained in APAR SE69832. Find your release of IBM i below to see if you need to take action or apply PTFs to benefit from this enhancement.

IBM i 7.1
IBM i 7.1 is no longer supported and no further PTFs are being created for it. SNDPTFORD at IBM i 7.1 will not work with encryption and customers need to use FixCentral instead.

IBM i 7.2
At IBM i 7.2, you must update your Electronic Service Agent (ESA) and Electronic Customer Support (ECS) configuration to use the new EDGE servers and enable encrypted communications over port 443. The steps to make this configuration change are provided in the document Electronic Service Agent (ESA) and Electronic Customer Support (ECS) VPN and HTTP Firewall Settings under the section Resolving the Problem > V7R2. Once this change has been made, apply PTF SI79293, if it is not already on the system.

IBM i 7.3
For IBM i 7.3, apply PTF SI68172.

IBM i 7.4 and 7.5
IBM i 7.4 and 7.5 already ship with an updated version of the ECC Common Client.  No PTFs are necessary.

The only other area of concern are users using custom APIs
The only other area of concern regarding this situation is a small number of customers that are known to be using APIs to directly download fixes from IBM and bypass FixCentral. Some of those customers were using unencrypted file transfer, and that will not be supported.