It’s not a thinner oil since it should have the same viscosity as the factory fill. It is a full synthethic that works better in any operating temperature range than the OE.

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2018 991 TT
2014 95B S

Porsches have had this symptom over many decades and different models (difficult shifting while cold). I wouldn’t say it’s ‘normal,’ but it’s common. There often isn’t a fix that’s easy to do. The Porsche gearboxes are built tougher than a regular street car, particular durable during high speed and tracking, and the side effect is compromised agility when cold.

I would check the current transmission fluid level to make sure it’s not dry. If it is dry, fill with Porsche standard fill. If that doesn’t work or the oil is at a OK level, then I would search for an oil fill that specifically addresses cold shifting. I would also make sure the shift linkages and shifter are in perfect working order. The difficulty in cold shifts is always present (cold oil is think, that’s just physics), but doubles or triples down if you are fighting friction for the shifting mechanism rubbing or not lining up.

If you find a different fluid, here’s what to watch out for: different fluid may be more slippery in general, which helps in cold shifting, but has an expense of increased wear at the extreme high temperate side, like when tracking the car in high heat or when shifting fast and hard after the car has fully warmed up (45+min trans temp). So if you like to track or shift hard/fast, I would keep the originally recommended oil fill and just deal with the cold shifting issue.

EDIT: I forgot to ask if stopping the car completely to engage any gear with the engine running makes cold shifting easier? If it’s impossible to shift when rolling along and the engine is on, and then while stopped you can grab any gear, it’s the probably thick/cold transmission fluid. If grabbing gears is hard with the engine off and stopped, now we have to start looking at the clutch components.