Hi!
Thonny does not provide such option.
It is customary to manually break lines in program code. Of course you should following syntax rules in doing so -- for example, when breaking a long comment you need to insert # in the beginning of each line; when breaking an expression, it needs to be in parentheses etc.
Automatic/soft linebreaks don't fit well with languages where linebreaks and indentation are part of the syntax.
Best regards,
Aivar