Page Title & h1 are different things. H1 you can always set using Product Description box or Collection Description box which I have show you in below image and Page title is the Meta title for SEO purpose for Google which you can edit from here as shown in the screenshot.
yes, you can use the brand name in Page title its good to use, but I prefer h1 you can use based on your page. for example, if the collection is about Watch then let's write something in h1 about watch title. which can help users to explore page.
I hope those clear your questions.
Using a brand name in title tags for each product is a better approach and therefore is a good SEO practice. The main objective behind this is the awareness and strength of the brand in the target market.
If its a well known brand then it can instantly make a difference in CTR in the search engine result pages. Brand name and the keywords are the top factors that helps in increasing the visibility of the website.
The major benefits of using brand name in page title are -
1) It can be used for the products unique selling proposition
2) No one will be able to outrank you for your product via search
3) It helps in increasing the visibility of your website.