Fix WordPress Mobile and Tablet Responsivness

I recently added a few custom components to my WordPress site and, while most of the desktop work looks okay, the responsive behaviour needs help. On both smartphones and tablets the main navigation either appear badly, renders half-off screen, or breaks its layout altogether. Its not on all devices and not on all situations, but I can ensure that the bugs are occures.

What I need is a clean, fully functional mobile and tablet responsive components
Here are some things i've noticed that are issues confirmed that needs to be fixed :
- Tablet menu layout looks bugged ( ex : on ipad pro format )
- Somes components display looks bugged because of bad layout/padding and margin, barely readable
- Slider component seems not well aligned, is currently aligne on the right side but requires to be centered
- The button "Book a Demo" is too big and looks bad on all mobile devices in the menu
- The menu looks broken with some lines on it overlaying on random situation / devices ( please refer to the screenshots )
- The menu pages and subpages when open on mobile looks broken too on some device ( i can confirm on my Pixel10 Fold ) that the components are overlapping, the navigation is bad, etc..
- Some titles and content appear way to big on the mobile phone
- The menu is not sticky on Desktop and Tablet but it is on mobile. It needs to be sticky everywhere and scroll / navigate well
- I have a proposal of efficient mobile menu navigation to make it effective and simple. Please refer to the screenshots "good-menu-proposition-layout1" and "good-menu-proposition-layout2"
- The testimonial components looks broken on some phones layout ( ex : Pixel10 Fold ) I can ensure (testimonials-bad.png screenshot ) . Please make it like on good layout, like on iphone 12 ( testimonials-good.png screenshot )