Known issue. This is a regression and it is being worked on with some urgency.
It involves bugs in both Lazarus and FPC, which makes it something not as ordinary as you would expect. This issue is quite complex.
At the moment it is not possible to compile Laz trunk with FPC trunk.
Be patient and do not complain: to find such issues is why we have public trunk/main versions.
(Although I am not really a fan of that, I am also guilty of using trunks all the time, but I know what it means)
The stable versions are OK of course, so use stable.
Don't file a bug report. The issue is known and bug reports are already filed, including by me and Martin.
If you want cutting edge, this is what sometimes happens.... Take note of that before you use trunk versions. They are everything but stable.
It has nothing to do with FpcUpDeLuxe. Just with Lazarus IDE and FPC.
You can follow the progress on the bug trackers (both Laz and FPC in this case)