Of the public domain options available the World English Bible might be the best modern English version available (though I don't use it myself). Here's an article I found online considering this question and they recommend the WEB:

https://inspiringtips.com/which-bible-versions-are-in-the-public-domain/

The article also discusses the New English Translation (NET) which is not public domain but can be used if it is not for compensation. It already comes with a lot of commentary notes which could be interesting. (I like this option myself):

"If you’re looking to reproduce and distribute an entire text of a bible version and charge money for it, you’re going to have to go with something in the public domain. However, if you’re not planning on being compensated for distribution, you can also check out one of my personal favorite translations: the New English Translation (NET). It’s a great translation, don’t get me wrong. But the real value of this version comes in the 60,932 translation notes, that comment on anything and everything, from detailed linguistic explanations, to cultural context of the scripture, to commentary-style interpretations, and so much more. It’s a fantastic resource for Bible readers everywhere, and it has probably the loosest copyright of other modern versions.

"You can copy, cite, and distribute the NET in full without any permission. The only caveat here is that you can’t charge money for it. So if you’re looking to create a Bible app or computer program, you can offer the NET as a free add-on. However, you can’t turn the NET text into a beautiful journaling Bible and sell it for a profit. There are a few other guidelines to follow, like how to attribute the text to the NET. If you’re interested, you can click here to read more about their copyright and distribution policy."