Turkeys primary rivals in the region, Greece and Egypt are going through some serious military buildup in last few years, maybe choosing S400 over F35 wasn't the best idea.
USA blocked transfer of F-35s to Turkey since 2015 , far before than S400 deal
I think U.S Congress also will block sale of F-16V to Turkey
Turkey focused on Air Defense Systems and Ballistic-Cruise Missiles to hurt Greece and Egypt
-- Turkey has already single stage Ballistic Missile technology up to 1.000 km
-- 800-1.400 km GEZGIN strategic Cruise Missile will be launched from land and naval platforms
-- ATMACA-K land based Cruise Missile and SOM air launched Cruise Missile
( indigenous KTJ-3200 turbojet engine enter service to power ATMACA and SOM for range of 500km )
-- 250 km ATMACA land based Anti-ship Missile
-- 250 km KUZGUN-TJ joint strike Missile with IIR seeker to hit Warships
-- 250 km SOM-C air launched Anti-ship Missile to hit Warships
-- 150 km TRLG-230 laser guided supersonic Missile to use by AKINCI UCAVs to hit Warships
-- 150 km AKBABA anti-radiation Missile
-- 150 km KGK-LR glide Bomb with IIR seeker to hit Warships
-- 100 km MRASHM Anti-ship Missile to use by UCAVs and unmanned combat Vessels
and 150 km RAMJET powered supersonic Anti-ship Missile to hit Warships
also 1.000 km KARGI anti-radiation Drone to hit Radars
AIR DEFENSE
-- Turkey has already developed KORKUT-35mm SPAAG , HISAR-A and HISAR-O Air Defense Systems to counter Cruise Missiles
-- 100 km HISAR-U and 150 km SIPER Air Defense Systems until 2024
-- Land based AD System based on GOKDOGAN a2a Missile .. ( similar to NASAMS )
-- S400 Air Defense Systems .. ( Turkey may buy 2nd batch of S400s )
-- TF-2000 class Destroyer with 64 cells VLS to carry 150 km SIPER air defense missiles
AIR FORCE
-- 163 CCIP modernized F-16 block52 armed with 120km AIM-120C7 air to air Missile
-- 29 F-16 block50+ armed with land attack Missiles like 280 km SLAM-ER
-- Turkey modernize 35 F-16s with national AESA Radar and Weapons including 100km GOKDOGAN Air to Air Missile
-- AKINCI UCAVs to carry AESA Radar and 100km GOKDOGAN Air to Air Missile to hit UCAVs and Attack Helicopters
-- MIUS unmanned Fighter Jet to carry AESA Radar and 100km GOKDOGAN Air to Air Missile
and F-16s , MIUS will carry RAMJET powered long range Air to Air Missile GOKHAN ...( similar to METEOR )
so, without F-35s , still Turkey to have great fire power and deterrence until the TFX air superiority Fighter Jet squadrons by 2035
btw Greece buys 3 Belharra Frigates and Turkey to build 31 new Warships
even Belharra Frigate can not enter Turkish EEZ in a conflict .. Thanks to hundreds of HARPOON , ATMACA , SOM-C , KUZGUN-TJ , AKBABA , HARM , SLAM-ER , TRLG-230 which can turn BELHARRA Frigate into crap of metal within hours