I don't think SQ F pax can access the LH F lounge, thus you will use the Senator lounge. I used the SEN lounge earlier this week...been there a number of times. Gets the job done but certainly nothing special. I always had time for a shower when on SQ25/26. As for access to the lounge during these times, I converted my Singapore vaccination info to a EUDCC QR certificate...had it saved to my phone home screen. Showed the EU cert and passport and was into the lounge in a flash.