We are using WP latest (v5.5.1).
I have just reproduced the error in a trial post, here.
Your YouTube block is the one toward the top, which I just added; a different YouTube block is below and functions properly.
What happens is that, once your block is inserted, all text in the edit window above the block cannot be selected (e,g., to format or add hyperlink). Any such formatting you see at present was done prior to adding your block.
I append below the edit code to your block and that immediately above, though I don’t see anything immediately off.
<!-- wp:paragraph -->
<p>The first thing I want to say is this (Adams 2020; Bolam et al. n.d.). <a rel="noreferrer noopener" href="https://www.catipsum.com/" target="_blank">Cat ipsum</a> dolor sit amet, spend all night ensuring people don't sleep sleep all day pretend not to be evil cat dog hate mouse eat string barf pillow no baths hate everything. Sugar, my siamese, stalks me (in a good way), day and night terrorize the hundred-and-twenty-pound rottweiler and steal his bed, not sorry catching very fast laser pointer then cats take over the world. </p>
<!-- /wp:paragraph -->
<!-- wp:paragraph -->
<p>For testing, here is another YouTube block, one I think is buggy...</p>
<!-- /wp:paragraph -->
<!-- wp:embedpress/youtube-block {"url":"https://www.youtube.com/watch?v=G8KpPw303PY","iframeSrc":"https://www.youtube.com/embed/G8KpPw303PY","mediaId":"G8KpPw303PY"} /-->