My first time connecting in ARN so just want to be sure:

LH business (FRA-ARN) connecting to TG business (ARN-BKK). US passport.
From the ARN website, it seems both LH and TG use terminal 5.
I have 1hour, 25 minutes scheduled as the layover. 12:15PM to 1:40PM

I assume there will be both security screen and immigration process, correct?

How difficult/time consuming is the connection at ARN?
Anything I need to be worried about or aware of?
Any priority lines for Business Class that I should be looking out for?

Thanks.

With a slight reservation that my info is a bit outdated, but here goes:

* No security, you will be exiting right into the departures (Schengen) area of the terminal. There will be a passport control when you go into the Non-Schengen area of the terminal. According to the latest information I have, Thai is using the F-pier at ARN, possibly gate F69, which can mean a lengthy walk of about 10-15 minutes (walking time only, no queueing time at passport control included) if your arrival gate is the furthest one away.

* As far as I know the Lounge used for TG passengers travelling in C is the SAS lounge, and it is located in the Schengen area of the terminal, close to Gate 1, so before passport control.

* No priority lanes for Business class passengers at passport control.

1 hour and 25 minutes should be plenty of time, so if you land on time or even with 30 minutes delay I wouldn't be worried.

That's great. Thanks for the helpful info.