Modal or Posts?

I am creating a website from scratch (no wp included), but instead of having separate pages for each post, i am using modals. What bothers me is if this would hurt on-page seo in any way, or is it safe to continue creating the website in same manner? Thanks!

The best thing if you dont generate/render pages using server languages (PHP etc..) and you keep them as .html files... but it makes it hard to manage your website...