In Odoo 16.0, a not perfect solution in Python + XML could be as follow, if one consider a native Odoo fields description = fields.Html().

Notice any HTML done from native description field will be lost if some edit the description from description_text field. In the other way, meaning modification of description field renders HTML tag with some added character (e.g. <strong>hello</strong> is replaced by *hello*). 

Python :

from odoo.tools import html2plaintext, plaintext2html
@api.depends('description')
def _compute_description_text(self):
    for task in self:
        task.description_text = html2plaintext(task.description)
def _inverse_description_text(self):
    for task in self:
        task.description = plaintext2html(task.description_text)

In the XML view:

<field name="description" position="replace">
	​<field name="description_text" />
</field>