The documentation for network.WLAN.isconnected() states:

In AP mode returns True when a station is connected. Returns False otherwise.

ref: http://docs.micropython.org/en/v1.13/library/network.WLAN.html#network.WLAN.isconnected

However, when I run the following code on a PYBD_SF6W:

import utime as time
import network
from urandom import randint
import machine

# Access Point
def make_ap():
    print("Access Point...")
    ap = network.WLAN(network.AP_IF)
    ap.config(essid='MyPyboard:{:04d}'.format(randint(1, 10000)))
    ap.active(True)

    while not ap.active():
        time.sleep(0.1)

    print("  AP_IF: {!r}".format(ap.ifconfig()))
    return ap

# ----- Mainline
print('machine.reset_cause()', machine.reset_cause())
ap = make_ap()  # network.WLAN in AP_IF mode
while True:
    time.sleep(1)
    print('isconnected()', ap.isconnected())

I get the output:

MicroPython v1.13-274-g49dd9ba1a on 2021-01-19; PYBD-SF6W with STM32F767IIK
Type "help()" for more information.
>>>
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== # pasted above code
machine.reset_cause() 1
Access Point...
  AP_IF: ('192.168.4.1', '255.255.255.0', '192.168.4.1', '0.0.0.0')
isconnected() True
isconnected() True
isconnected() True
DHCPS: client connected: MAC=66:bc:1c:1a:af:f1 IP=192.168.4.16
isconnected() True
isconnected() True
isconnected() True

What I would expect is that before the DHCP connection is made, before any stations are connected to the AP, isconnected() should return False.