Chris, thank you so much for your response. It looks like since client-side rendering is used, it builds virtual DOM and attaches events to make the page interactive, However, with SSR approach, the user could start viewing the page while all of that is happening.  Since I'm reviewing the website performance, SSR should be generally faster than client side rendering to the user. Even if Google still indexes majority of pages it doesn't mean that those pages will be ranked high because of the delayed page load. Thank you for much for sending me to the right direction. I didn't think of this option before you responded.

sleepcountry.ca uses Oracle Commerce Cloud which uses Knockout data-binds syntax to attach events to DOM elements like this (A <a id="s0207useresourcesinwidgets01"></a>Knockout custom binding named ‘widgetLocaleText’  - I am not familiar this technology stack):

Same applies to H1 tag - you can't find H1 tag in Source.

In short, the text binding causes the associated DOM element to display the text value of your parameter. Data binding is applied to all DOM elements on pages of sleepcountry.ca  even that this technique doesn't pass W3C markup validation: Error: Element title must not be empty.

MOZ reports that all H1 Tags are missing on ALL PAGES of the site. Same is reported by Semrush and other respected services. However, it seems like Google automatically adds tagging to all data-bind(ed) elements including Title! site:sleepcountry.ca

I'm no expert in Oracle Commerce Cloud or Knockout, but I'm confused.
QUESTION: Does this data-bind hurt organic search and if it does, why Google still sees all TITLES while Moz and other services report it as a major problem - titles are missing. ?

Thank you so much in advance! (I'm not an SEO expert but this problem might be related to my project)