Switching to WP-How to handle .htm pages: 301’s or permalink?

This HTML website is going to be redesigned in WordPress. All pages have “.htm” extensions and the homepage is “/index.htm”.

I’ve found sources suggesting to add .htm to the permalink structure of the new site’s pages, but that CANNOT be the only way to not lose page rank, right?

Since they’re keeping the same domain name, will 301 Redirects only cause a temporary drop in ranking?

And if redirect is the best practice here, is there any advantage to doing “RewriteCond” & “RewriteRule” vs. “Redirect 301” in .htaccess?

Thank you in advance!

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