Yes Plans C and F are not available to anyone after January 1, 2020 unless you already have one of those plans according to Medicare.gov. So the best plan a person can get at this point if you are not on one of those plans is probably Plan G.
I like the side by side comparisons that Medicare.gov has on the supplement plans. Any insurance can sell one of these plans and charge whatever premium, but they all have to follow the same rules for each plan.
Quoted from the Medicare site (I'm sure our government had a hand in this)
https://www.medicare.gov/suppl...
"Note:
As of January 1, 2020, Medigap plans sold to new people with Medicare aren't allowed to cover the Part B deductible. Because of this, Plans C and F are not available to people new to Medicare starting on January 1, 2020. If you already have either of these 2 plans (or the high deductible version of Plan F) or are covered by one of these plans before January 1, 2020, you'll be able to keep your plan. If you were eligible for Medicare before January 1, 2020, but not yet enrolled, you may be able to buy one of these plans."