Even though you've set sanitize=False on the HTML field, Odoo may still be applying some additional sanitization or escaping to the HTML content, which could prevent the script from running

To achieve the functionality you're looking for, you can consider use of an Odoo Widget with JavaScript

You can find the example from module im_livechat

script_external = fields.Html( 'Script (external)' , compute = '_compute_script_external' , store = False , readonly = True , sanitize = False )

def _compute_script_external(self):
    values = {
        "dbname": self._cr.dbname,
    }
    for record in self:

        values["channel_id"] = record.id
        values["url"] = record.get_base_url()
        record.script_external = self.env['ir.qweb']._render('im_livechat.external_loader', values) if record.id else False

<template id ="external_loader" name ="Livechat : external_script field of livechat channel" > 
    <!-- the loader --> 
    <script t-attf-src ="{{url}}/im_livechat/loader/{{channel_id }}" type ="text/javascript" /> 
    <!-- js of all the required lib (internal and external) --> 
    <script t-attf-src ="{{url}}/im_livechat/assets_embed.js " type ="text/javascript" /> 
</template>