Custom theme doesn’t work

Hi,

I’m rookie in WordPress and especially in designing a theme. I went through some tutorials and I have even done a really simple theme. Today, I’ve tried to design something more ‘complicated’ and I found some html templates at freecsstemplates. Now I’m stuck because I have done everything correctly (not really if it’s not working..) and the theme doesn’t show up in Appearance -> Themes (it does show description and gives opportunity to active/preview theme but when you do that, it goes blank, without any html).

I assume that there may be some mistakes in the code but I just can’t find anything.

I have also checked google and found some similar problems but that’s not solution for me.
https://www.vanseodesign.com/wordpress/wp-page-templates-dropdown/
https://www.elitefreelancing.com/wordpress/custom-page-templates-not-showing-up-in-wordpress/
and
https://www.zachgraeve.com/2009/01/14/wordpress-27-page-templates-not-working/

I can send .zip with template if needed.

Best regards
Adam