There are a lot of frozen French fry recipes on Google and YouTube, but none stay crispy after defrost. I have tried many. After 2-4 month they become soft and pale. I doubt there are some chemicals which can keep their taste and crispy texture. Such as potatopro or McCain supplier. Any suggestions?
Most likely, your issue is that your fries don't freeze quickly enough!
First of all, potatoes are VERY tricky for freezing anyway: their cell-structure takes REALLY badly to freezing, making them change texture and sometimes taste a lot.
The problem is reduced, but not removed, by cooking them first, but even then, they tend to react badly.
Now, what do commercial fries have that you don't? They can actually do shock-freezing! This means they can freeze their fries REALLY quickly, which highly reduces the damage to the cells. So, sadly your best shot may be: buy some dry ice to use for freezing your fries.