All you have to do is create a Custom HTML block, where you can add your text and this code where the year needs to go (in this case for a business founded in 1984):
<script>document.write(new Date().getFullYear() - 1984)</script>
Here's what it looks like in practice, wrapped in a <blockquote> element with a bit of text:
<blockquote class="wp-block-quote"><p>Founded <script>document.write(new Date().getFullYear() - 1984)</script> years ago</p></blockquote>
Founded years ago
And there you have it – that number of years will automatically increase by 1 on January 1st!