I have tried a number of different options:

OPTION 1:

<div style=”width: 50%; float: left; margin: 0 10px 5px 0;”>

</div>

This results in an embedded video wrapped to the left, text to the right like I want in the normal web page, but the amp page results in a video box with a broken link.
—————————————————————————————-
OPTION 2

<div style=”width: 50%; float: left; margin: 0 10px 5px 0;”>

[video src="https://www.youtube.com/watch?v=tFtjQKLElTQ"]

</div>

This also looks good on a normal webpage but the video <div> box takes up 90% of the width, has a broken video link and covers up the text wrapped to the right side of the post.
—————————————————————————————
OPTION 3:

<div style=”width: 50%; float: left; margin: 0 10px 5px 0;”>

[embed]https://www.youtube.com/watch?v=tFtjQKLElTQ[/embed]

</div>

This also looks good on a standard web page, but the amp page has no embedded video and results in the same “Content Mismatch” error on Google Search Console.
—————————————————————————————-

I am going to disable tagdiv amp plugin and try the automattic one instead. Will return to tagdiv plugin if I don’t come right there or try again later.

Thanks Bogdan B,
Using the oembed option fixes the amp issue.
Unfortunately this seems to mean that I will have to give up all the formatting I was using the <div> and <iframe> for. I was using the <div> to align the video to the left and wrap my text to the right. This embed, even if I use [embed] or [video] ignores any width settings and the video takes up the full width of my post.

Thank you, I will give that a try 🙂

Upon further investigation, I found that the tagdiv amp plugin is converting my iframe to amp-iframe but because I am using the iframe to embed a youtube video, I need it converted to amp-youtube instead.
Is there any way I can fix this?