Rename a tablename using db_schema(Declarative schema) in Magento 2.

In Magento 2, You can create a new table using db_schema.xml file. After creating a table you want to rename a table name, You can rename a table using declarative schema.

New Table(mycustom_table) db_schema.xml file,

<?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="mycustom_table" onCreate="migrateDataFromAnotherTable(new_declarative_table)">
        <column xsi:type="int" name="entity_id" padding="10" unsigned="true" nullable="false" identity="true"
                comment="Entity Id"/>
        <column xsi:type="varchar" name="fullname" nullable="true" length="50" comment="Full name"/>
        <column xsi:type="varchar" name="email" nullable="true" length="255" comment="Email"/>
        <column xsi:type="smallint" name="store_id" padding="5" unsigned="true" nullable="true" identity="false"
                default="0" comment="Store Id"/>
    </table>
</schema>

Now you must have to run generate-whitelist command to generate db_schema_whitelist.json file,

php bin/magento setup:db-declaration:generate-whitelist –module-name=Vendorname_Packagename

Where Vendorname_Packagename is your Vendor and Packagename.
Now you can change the table name using below tag in the XML file,

<table name=”rename_tablename” onCreate=”migrateDataFromAnotherTable(mycustom_table)”>

where rename_tablename is your new table name and mycustom_table is your old table name in the above tag.

The new db_schema.xml file will be,

<?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="rename_tablename" onCreate="migrateDataFromAnotherTable(mycustom_table)">
        <column xsi:type="int" name="entity_id" padding="10" unsigned="true" nullable="false" identity="true"
                comment="Entity Id"/>
        <column xsi:type="varchar" name="fullname" nullable="true" length="50" comment="Full name"/>
        <column xsi:type="varchar" name="email" nullable="true" length="255" comment="Email"/>
        <column xsi:type="smallint" name="store_id" padding="5" unsigned="true" nullable="true" identity="false"
                default="0" comment="Store Id"/>
    </table>
</schema>

Run command,
php bin/magento setup:upgrade

You can check your table name is replaced with a new name.