First of all, you have made a few driver parameter selections for iwlwifi, a wireless driver for Intel devices. You have none; yours is a Realtek.
While the parameter selections do no harm, they are needless and merely take up space. I suggest that you remove them.
sudo rm /etc/modprobe.d/iwlwifi-options.conf
Second, I shall be very surprised if the device doesn’t support 5 gHz channels; let’s confirm:
sudo iwlist freq
Does your router support 5 gHz?
nmcli device wifi list
If so, I suggest that you rename the 5 gHz band in the administration pages of the router, something like redhu5 or some such and connect to it instead.
Next, you tried ant_sel=2 with no success. Please try ant_sel=1:
echo "options rtl8723be ant_sel=1" | sudo tee /etc/modprobe.d/rtl8723-ant-sel.conf
Reboot and see if there is any improvement.
Finally, as has been suggested, try setting a fixed channel in your router, either 1, 6 or 11. After making any change, reboot the router. See if any of these brings improvement.
Best Answer
I have the same module in HP Probook 440-G5 and have the same issue, for what I've found, it is not implemented yet :(. So we need to wait until someone implements them.