Mobile Responsiveness Issues

I don't think it would. I tried searching if it has any effect, but I can't find one.

It's just a div though. What would be bad about it is if there's a lot on a page since it still counts as a DOM element. Having too many DOM elements isn't good performance-wise.

a fourth option would be this code:

.single-post .entry-content  p:after {
content: "";
display:block;
height: 40px;
}

It adds a pseudo-element which isn't counted as a DOM element.

Depending on your post's size one option may be beneficial over another.

Thanks Fernando & Team for the help.

You're welcome, Anant!