Go to Blocks>product.title.liquid and find this line
{% assign product_title = ‘<p role=”heading” aria-level=”3″>’ | append: closest.product.title | append: ‘</p>’ %}
Replace with this
{% assign title_words = closest.product.title | split: ‘ ‘ %}
{% if title_words.size > 25 %}
{% assign short_title = title_words | slice: 0, 25 | join: ‘ ‘ | append: ‘…’ %}
{% else %}
{% assign short_title = closest.product.title %}
{% endif %}
{% assign product_title = ‘<p role=”heading” aria-level=”3″>’ | append: short_title | append: ‘</p>’ %}
25 is the value you need to change accordingly