Just because the G.Skill Trident Z RGB ram is not on the QVL (Qualified Vendors List) doesn't mean it will not work on the Asus STRIX X370-F, it just means Asus has not tested it, so Asus will not guarantee it will work. They do not test all ram available on the market. G.Skill has a very good reputation so i would not worry about using their ram. Also the size of the ram [4GB or 8GB] will not make any difference.
Just because the G.Skill Trident Z RGB ram is not on the QVL (Qualified Vendors List) doesn't mean it will not work on the Asus STRIX X370-F, it just means Asus has not tested it, so Asus will not guarantee it will work. They do not test all ram available on the market. G.Skill has a very good reputation so i would not worry about using their ram. Also the size of the ram [4GB or 8GB] will not make any difference.
G.Skill F4-3200C14D-16GTZ is on the list. Your F4-3200C14D-16GTZR is the same ram with RGB. They are virtually identical.