Responsive.menu (both free and pro) are now compatible with WordPress 5.3.x and PHP 7.4. I know we are a little late to the party, but we are here now. Update your plugins via the WordPress backend.
We have been pushing updates to free and pro versions lately and have been planning for significant update next month. If you have any suggestion, feel free to enter your submission into our roadmap at https://responsive-menu.public.makerkit.co/
For support reachout to us via https://support.responsive.menu/ and for any other queries write us at firstname.lastname@example.org
Bonus: To get an instant 10% discount off of pro version use coupon code 10OFF