Select Place all certificates in the following store (second option), then click Browse…
A new window will pop up, select Trusted root certification authorities and click Ok
Click Next
Click Finish
If everything else fails…
…you can try to remove all existing Akatsuki certificates and install the certificate again. Follow these steps:
Press Win+R
Type mmc certmgr.msc in the run box and press enter to open the Certificate Manager
Select Trusted root certification authorities on the left
Select Certificates on the right
You should see some Akatsuki and some *.ppy.sh entries in the list. Select them, right click and click on Delete
Select all the positive options (Ok/Yes etc)
Restart the switcher, click on Inspect, then choose Install certificate, then Yes
Click on Test Akatsuki connection and you should see “OK” for every domains If the inspect dialog is fine but you still can’t connect to Akatsuki from the game client, try running osu! as administrator.