Long Bootstrap HTML form and Javascript validation - mobile friendly

I'm looking for someone to improve the mobile friendlyness of an existing form. The current form works well on desktop but needs to work better on mobile devices. No need to worry about back end processing this is all about user friendlyness and browser side validation. Must be Bootstrap 5 and I would prefer that our own simple existing JS validation library was used and improved. It must be easily maintainable and I want to avoid external libraries with potential security vulnerabilities.