Thanks to all for answers, but this methods what all of provide are not display values after they were stored into ir config parameter module DB. The actual problem is that after reloading the page or re-enter in Settings page after saving the values , the selected before fields values are not shown. I have checked DB of ir config parameter and it`s sure that values are correctly stored. Maybe its for security reasons Odoo has disable this in Odoo 16. Thanks in advance for answers.

``` python

class ResConfigSettings(models.TransientModel):

​_inherit = 'res.config.settings'

​drop_down = fields.Many2one('group.info', readonly=False)
​allowed_user_ids = fields.Many2many('user.info', readonly=False, store=True)

​def get_values(self):

​ ​res = super(ResConfigSettings, self).get_values()
​ ​config_parameter = self.env['ir.config_parameter'].sudo()

​ ​group_def =config_parameter.get_param('group.info.drop_down')

​ ​allowed_user=config_parameter.get_param('bot_module.allowed_user_ids')
​ ​allowed_user_ids = []

​ ​if allowed_user_default and isinstance(allowed_user_default, str):

​ ​ ​allowed_user_ids = literal_eval(allowed_user)
​ ​res.update({

​ ​ ​'drop_down': group_def,'

​ ​ ​allowed_user_ids': [(6, 0, allowed_user_ids)],

​ ​})

​ ​return res

​def set_values(self):
​ ​res = super(ResConfigSettings, self).set_values()
​ ​config_parameter = self.env['ir.config_parameter'].sudo()

​ ​config_parameter.set_param('group.info.drop_down', self.drop_down.id)
​ ​config_parameter.set_param(

​ ​'bot_module.allowed_user_id',

​ ​self.allowed_user_ids.ids)
​ ​return res

```

Here is a peace of code that I use to set and get values.

Thanks to everybody for the answers. I solve my issue for Many2many a many2one :
config_parameter = self.env['ir.config_parameter'].sudo()
config_parameter.set_param('user_client.keywords', self.keywords.ids)
config_parameter.set_param('user_client.group_and_chat', self.group.ids)