Image alt text not counting towards SEO

Site URL: https://www.henamedherarya.com/

Hello,

I use Gallery Blocks to showcase my photography, usually the "Stacked" option. I recently discovered that what is written in each image's Title and Description does not count towards my website's SEO unless I select "Show Title and Description" in the gallery options. I'm confused because I thought the T+D counted towards SEO even if the information didn't show on the page. Is there a way to make the T+D count towards SEO without showing it all on the page or forcing me to select a different Gallery style? I am familiar with "hiding" the caption under individual image blocks but Galleries seem to behave differently.

Thank you in advance for any assistance.