.htaccess rewrite rule not working for index.php - .htaccess

Question

I am trying to use pretty urls so https://example.com/event/1/dog-singing will load https://example.com/events?action=show&id=1
I added the following code to my .htaccess:
RewriteEngine On
RewriteBase /
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteRule ^event/([^/]*)/?(.*)$ events?action=show&id=$1 [L,NC]
I get a 404 page.
I tried using
RewriteRule ^event/([^/]*)/?(.*)$ index\.php/events?action=show&id=$1 [L,NC]
Same 404 page.
The below rewrite works. But I don't want to load the script from the subdirectory.
RewriteRule ^event/([^/]*)/?(.*)$ wp-content/plugins/testplugin/testplugin\.php?action=show&id=$1 [L,NC]
The one below also works. But it changes the pretty url in the address bar.
RewriteRule ^event/([^/]*)/?(.*)$ https://example.com/events?action=show&id=$1 [L,NC]
EDIT
Here is the full .htaccess
RewriteEngine On
RewriteBase /
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteCond %{SCRIPT_FILENAME} !-f
RewriteRule ^event/([^/]*)/[^/]*/?$ index.php?action=show&id=$1 [QSA,L,NC]
RewriteRule ^register/([^/]*)/?(.*)$ wp-content/plugins/testplugin/testplugin\.php?action=register&event=$1&name=$2 [L]
# BEGIN WordPress
# The directives (lines) between "BEGIN WordPress" and "END WordPress" are
# dynamically generated, and should only be modified via WordPress filters.
# Any changes to the directives between these markers will be overwritten.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress