Fixed gear steel frame from AliExpress I would like to build my own fixed gear bike.
I want a steel frame, I know different quality of steel and I want to avoid HI-Ten.
I will be mostly for urban cycling (pavements) and I would take rougher paths from time to time. So I need wheels with at least 28mm large (so not a tight fork).
I live in Switzerland and looking on the Internet, I didn't find my frame.
I never bought on AliExpress, I am afraid I will have bad surprise (counterfeit) while I was looking for this frame :
French: https://fr.aliexpress.com/item/1005001398900346.html 
English: https://www.aliexpress.com/item/1005001398900346.html 
German: https://de.aliexpress.com/item/1005001398900346.html
I mean what is strange is that they say the type of the frame is : Steel Cr-Mo 4130/525/725/Tube Reynolds Columbus.
What does it means to put at least 3 kind of steels and one of the best two manufacturers of frame in the world (Reynolds and Comlombus) ? (they made a mistake writing Columbus ... but I don't know if it's because of poor translation)   Is it serious ?
No, it is not serious, you should not believe these descriptions. They just try to attract people searching various terms.
There are indeed many counterfeits in these shops. When they claim so much different stuff at once it is quite certain.
That does not mean that the frame would not work, but if shopping in Asia it is better to shop from brands that do not pretend they are something else and sell under their own Asian brands.