step 1 - turn on developer mode (on the bottom of settings)

step 2 - go to 'menu items' (just start typing on the main screen)

step 3 - make new menu item like this:

• Menu: your name that you want to have displayed on home
• Action: ir.actions.act_url
• Sequence: the lower you get, the higher the icon will be

step 4 - save the menu item, so you can type in your custom product URL in the Action section after the 'ir.action.act_url' 

step 5 - name your new URL Action (like below for example 'MyCustomProductUrl' and hit 'Create and edit'

step 6 - get the link to your product - in my case odoo v18 online it will be odoo/action-281/1 (id of product is 1)

step 7 - put in the details as follows:

• Binding Model: Product
• Binding View Types: form
• Action URL: odoo/action-281/1
• Action Target: ## I think you will know which one you prefer

step 8 - access rights - depending on who you want to see the icon you can add groups (for example only for inventory supervisor, add the group in menu items)

step 9 - customization  - you can change icon if you want - if not it will be the 'boxed !'

if you want to use one of the existing odoo ones you can type in the location in odoo of it in the yellow field, or just upload a custom one from your hard drive.

hope this helps...

Edit:

to edit action you can click on the arrow icon