The current Intel AX201 driver from Microsoft (21.40.1.3) has a problem where after sleep the Wi-Fi speed is severely reduced. See for example here.
Workaround I found:

1. Go to the hardware manager -> network adapter -> Intel AX201 -> Advanced -> MIMO power save mode -> Change "Auto SMPS" to "No SMPS". While this resulted in the bug occurring less frequently, only changing the setting to "Static SMPS" (-> disabling MIMO) eliminated the problem entirely for me.
   
2. (Optional) Go to the Windows Settings App -> System -> Power & Sleep -> When my PC is asleep and on battery power, disconnect from network -> Change "Never" to "Always"

Explanation of the bug:
The new Intel AX201 adapter has 2x2 MIMO, basically double the antennas for double the speed (if your router supports it). Now in standby Dynamic SMPS disables one antenna and the other antenna goes to a low power state. However the bug is that after waking up the device from standby, the second antenna is not activated and the other antenna remains in the low power state resulting in severely reduced speeds, higher latency, ...
Since disabling SMPS leads to higher power consumption when in standby (both antennas remain active, possibly in a higher power state than necessary) I have included the second step where you can simply disable Wi-Fi while in standby. If you change the setting to "Static SMPS" this shouldn't be necessary, however you lose MIMO, ergo up to 50% slower speed.

Obviously this is just a workaround but imo still better than using hibernation instead of standby to avoid the problem. Hopefully Microsoft/Intel will fix this Wi-Fi standby bug caused by MIMO soon.