https breaking site?

Hi,

I set up a new site earlier this week, created a few pages and templates in Elementor and installed a few plugins (among those, Elementor Pro). Then I got round to install Letsencrypt on my domain and Wordfence (if things take off the site could be a target of attack). Could it be that installing Letsencrypt on my domain would break the entire WP site?
After battling for a day I still have two main problems.

1 – I can’t install any plugins – I get a message about FTP servers and user name. I’ve never used FTP on any of my sites before, and I don’t know why it should start nagging me about FTP now (it didn’t when I installed to the site running under non-encrypted http).

2- Elementor is unable to edit either pages or templates I used to set up the site while using non-encrypted http.

Have I f***ed up somewhere? And how do I fix this mess?
(Given it has something to do with https rather than http).