How to fix the error ERR_TOO_MANY_REDIRECTS - HTML WEBSITE

I have been showing the error ERR_TOO_MANY_REDIRECTSERR_TOO_MANY_REDIRECTS on my website for some time.

Everything was fine up to a point, I have no idea why, do you have any ideas?

Here is my .htaccess code:

RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.+)/$ /$1 [R=301,L,NE]

I will add that I have SSL from Let's Encrypt.