OK, I researched it. This is what I found and this is what I did to solve the blocking problem. It’s easier than I thought.
What I found:
1) More and more people who know a lot more than I do about this subject, say that for most websites, a robot txt file isn’t even needed anymore. Why? Because the only bots that care about what it says are the good guys like Google that it’s blocking. The bad bots don’t say “I want to hack a site but look, they don’t want me to go to this file, shucks”. The robot txt file is just a suggestion, some bots don’t even bother to look at it.
2) Yoast (I don’t use that plugin anymore but I have a lot of respect for them) wrote that he doesn’t block WP Admin or WP includes at all anymore.
See: https://yoast.com/wordpress-robots-txt-example/
I went to yoast.com and looked at their /robots.txt and sure enough, they only block something to do with affiliates. In his post, he said that when you delete the robot txt file, WP will automatically at something. WP isn’t stupid.
So I tested it. I deleted my robot txt file that my seo plugin added and checked my /robots.txt and sure enough, a new file was there:
User-agent: *
Disallow: /wp-admin/
Sitemap: https://www.(removed for privacy).com/sitemap.xml.gz
I went to google webmasters and did a fetch as google AND render (you have to choose that option). Result? No more blocked css or java.
I must say I had the confidence to do this because I have Wordfence (free) an excellent plugin that was not the cause of this issue for me, and Bulletproof Security (free) another excellent security plugin and have made use of BPS’s custom codes. I also have a CDN with firewall (paid) that keeps some bad actors from even getting to my site.
I can’t guarantee this will work for you but it’s easy enough to try and test if you’ve signed up with Google Webmasters. It’s free and you just have to verify you own your website.