Hi @chilipepp2020
If you use Approval, then the ‘custom responses’ is responses customized by flow creator and not something approvers can type as plain text. Approvers can only choose those response options you customized.
As a workaround, if approvers want to manually text something, after choosing an customized response option, they can type in ‘Comments’ as below:

If you want to reference approvers’ comments in flow, you can use the dynamic content ‘Responses Comments’ from the action ‘Start and wait for an approval’ as below:

Best Regards,
Community Support Team _ Kira Xie
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.