This should have explained you already that there is no connection between the forum and the sites where you tried to upload your image...
I think I had bad choices of word. I was able to upload the file on image hosting site without any issue, it allowed me to upload webp file if I'm not mistaken but when I implemented the bbcode on bitcointalk, the image wasn't displayed here.
Ohhhh, now I understand what you meant! Yes, this changes things completely... But are you sure you actually managed to upload the .webp picture on that site? Do you remember, at least, what site it was? I am asking because not many websites accepts .webp images and, perhaps, you do not remember well... As you saw, in my earlier post, imgur also does not allow uploading .webp images, notImgBB. I mean maybe we could try this again, following exact steps you made first, in order to see exactly where the problem is.
I see. I have used gif, png and jpg. Can't remember if I have ever used JPEG or not.
I used .jpeg today and it works fine. .gif and .png also work for sure (unless dimension limit of 2.5 MB is reached).