SoloLearn Code Playground has input type set to email. Why?
When you enter any email address in email field then your keyboard will show '@' symbol on left of space and all the symbols on the '.' key are replaced by '.com', '.org', etc. It all happens while in code playground also. Also while typing keyboard doesn't show suggestions on the top. This all make coding inefficient in playground using software keyboard.
This problem arise on Gboard. I don't know about this problem on other keyboards. So it should be fixed. I don't think it would take much effort for the SoloLearn developers.
I quoted your question Description "This problem arise on Gboard ..."
You were the one who mentioned that in the first place. I have the same problem when I'm using built-in keyboard app, but not when using alternative keyboard app.
If you read the thread I linked, or did a further search you will see this is no new case. Nevertheless you are free to e-mail the development team if you wish to.
Gboard is known to have a thing with Code Playground, I found this thread from a search by keyword 'GBoard', I think you can find more similar topic about GBoard problem in search bar.
In summary, most responses suggested to use another keyboard app.