There is no formal ICANN TLD list. The PSL is your best shot. So it is actually wrong to assume that your situation is the sole purpose.

For instance, https://data.iana.org/TLD/tlds-alpha-by-domain.txt

Where is .co.uk ? That is - for all intents and purposes - considered a TLD.

So PSL is currently doing double-duty and the distinction is very important.