Redirect with no slash to .html?

Question

htaccess

Good afternoon, there are not many articles on the site, the wordpress engine, change the link from .html to the end of the articles, before that I did a redirect with a slash to without a slash, how now to make the link redirect to the .html link, and is it necessary at all .
right now it's like this
# remove the slash at the end of the address
RewriteCond %{HTTP_HOST} (.*)
RewriteCond %{REQUEST_URI} /$ [NC]
RewriteCond %{REQUEST_URI} !^/wp-admin(/(.*)|$)
RewriteRule ^(.*)(/)$ $1 [L,R=301]
Redirect 301 /category https://site.ru
RewriteCond %{REQUEST_URI} ^/category/.*
RewriteRule ^category/(.*)$ http: //%{HTTP_HOST}/$1/? [R=301,L]
There is also a problem, in one section, the site.ru/online-testy link, if you click on it, transfers to site.ru/online-testy.html