You change that Field length from Custom module.
Create db_schema.xml
at your module and add below code:
<?xml version="1.0"?>
<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
<table name="catalogrule_product" resource="default" >
<column xsi:type="varchar" name="action_operator" nullable="true" length="50" default="to_fixed"
comment="Action Operator"/>
</table>
</schema>
And your module should depend on Magento_CatalogRule
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
<module name="{VendorName_ModuleName}">
<sequence>
<module name="Magento_CatalogRule"/>
</sequence>
</module>
</config>