Originally Posted by st8dm

try loungebuddy app (hope I won't be killed for ad, i'm just a regular guy and they have millions of downloads).
It always saves me from a lot of troubles and gives accurate information about lounges status (open/closed).
Nowadays things are changing without notice.
Also, with covid, lounges modified their access times. You might find lounges closed at 5PM without notice.

As a rule of thumb, the most exclusive the lounge - the better.
If you fly lufthansa (which most likely is the case) try lufthansa senator lounges.
There are plenty, open, and still rockin',

If you fly other Star Alliance airline, you might find disappointing the distance between your gate and the lounge location. FRA is not small, in worst case scenario you up to 45m to walk from one point to another.
I skipped a couple of lounges access because of this reason.

In FRA, you have two Lufthansa business lounges for Schengen area:
Terminal 1, concourse A, gate 26 (06:00 - 21:30) and
Terminal 1, concourse A, gate 13 (07:00 - 21:30)

For terminal 2 are other options - please let us know if you still need help.

hope this helps.