<record id="test_rule_on_write" model="base.automation">
<field name="name">Base Automation: test rule on write</field>
<field name="model_id" ref="base_automation.model_base_automation_lead_test"/>
<field name="state">code</field>
<field name="code" eval="'records.write({\'user_id\': %s})' % ref('base.user_demo')"/>
<field name="trigger">on_write</field>
<field name="active" eval="True"/>
<field name="model_id" ref="base_automation.model_base_automation_lead_test"/>
<field name="filter_domain">[('state', '=', 'done')]</field>
<field name="filter_pre_domain">[('state', '=', 'open')]</field>
</record>

OR

.xml file

<record id="test_rule_on_write" model="base.automation">
<field name="name">Base Automation: test rule on write</field>
<field name="model_id" ref="base_automation.model_base_automation_lead_test"/>
<field name="state">code</field>
<field name="trigger">on_write</field>
<field name="active" eval="True"/>
<field name="model_id" ref="base_automation.model_base_automation_lead_test"/>
<field name="filter_domain">[('state', '=', 'done')]</field>
<field name="filter_pre_domain">[('state', '=', 'open')]</field>
<field name="code">
if records:
records._my_func()
</field>
</record>

.py file

def _my_func(self):
add your code here....

Hey Jainesh !
Thankyou so much for your help, but unfortunately, I already tried this.
I get the same empty RPC_Error as I get on raise UserError('something').

On the other Hand this works well :
if record['service_state'] == "verzug_1":
env['esc.sst'].browse(record['id']).copy({'parent_id':record['id'],'service_state':'verzug_1','fk_status':3})