Hello Sunsaan and welcome to AbanteCart forum.

It is not very clear what you set up from the screenshot, but my guess it a category menu what you show.
You can only add categories to the "category" menu.

In original template, there is a menu (home icon) on the left side of the bar. I do not see it on your screenshot.
You can assign specials to that menu. See my screenshot.

If you still need to add a link in the menu that you showed, you will need to edit the category block code or add new block to the right of the category and add link this new block.
Blocks are managed in the layout section.

Default AbanteCart does not have multiple sellers solution. There is only multiple store.  Are you using some customization or extension?

Can you share your HTML/CSS or post a link?

You need to edit below line in fine public_html/extensions/bootstrap5/storefront/view/bootstrap5/template/common/header.tpl
Around line 3 there is a code below
<div class="mb-auto col-12 col-md-2 d-flex flex-wrap flex-md-nowrap justify-content-between"       

You need to set a 100% width here and set justify-content-center

AbanteCart v2 is open source as well.

https://github.com/abantecart/abantecart_2.0

This is a different Architecture application with support of Laravel/Eloquet and other tools.
Read about it here https://managed.abantecart.com/custom-ecommerce.html

We run this platform for our larger clients and our support will be only for paid customers with larger scale ecommerce and custom business workflows. 

Hello andmoss123,

There are multiple aspects here and I try to understand what you ask.
I assume you want to enter price with the the tax and automatically recalculate to base price without tax.

Challenge is with multi regional stores, as tax class is connected to the customer's location (delivery address).
If your business is only in one location it will not be a problem, but we need to cover all the scenarios in the platform. 

I think this can be solved with adding 2 extra fields. Price Including tax and tax class/value selection
After entering price with tax, base price will be calculated based on selected tax class/value
This can be done with the JavaScript on tax class/value selection event.
After base price is calculated and form is saved, the storefront will use base price with tax class appropriate to the location.

See similar form image from prestashop

Does this work or you looking for something different?

You can set both URL settings to use HTTPS
Go to system -> settings -> store details