The use of @api.depends('user_ids') in the _compute_user_ids method appears unnecessary and might not be the best approach for the intended functionality. The @api.depends decorator is typically used when the computation depends on the field specified, but in this case, you might want to consider using an @api.onchange method instead. This will trigger the logic when the user_ids field is modified, which seems more appropriate for updating subscriptions.

Here's a revised approach using @api.onchange:

user_ids = fields.Many2many(

    'res.users', 

    string='Users', 

    store=True, 

    readonly=False

)

@api.onchange('user_ids')

def _onchange_user_ids(self):

    for rec in self:

        user_list = [user.id for user in rec.user_ids]

        rec.message_subscribe(partner_ids=user_list)