I bought Bryce 7 Pro a while ago from Daz 3D's website. Today I re-downloaded it. What came was:-
BryceLightning_7.1.0.109_Win.exe , 11,116 megabytes
BryceProContent_7.0.0.19_Win.exe , 17,639 megabytes
Which of these two should I install first?
Those two files look remarkably small to contain a program with Bryce's capabilities.
When I try to install Bryce 7, it says that I have Bryce already installed and that it must uninstall the old installation first.
But attempted uninstallation of Bryce 7 fails.
So I can't install my Bryce 7.
A look at Control Panel/All Control Panel Items/Programs and Features ( / should be backslash) shows a long list of installed programs but nothing with "Bryce" in its name. There is no Bryce icon on my desktop. I have Windows 11.

Try this thread Bryce Sticky Thread

You also might want to try this one too

When I try to install from my BryceProContent_7.0.0.19_Win.exe , this happens:

It asks me to (1) specify an installation path or (2) to select to select a path from a list.
If (1), it says that it can't find Bryce at the chosen location..
If (2), it shows a list with no entries in it.

At this point I'd be tempted to search all my drives for anything Bryce related. Unfortunately I don't use win11 so I can't help much there. You might want to use CCleaner or similar to clear out residue files and junk and start over.

when did win 11 happen...still on 10 here.

You might want to uninstall whatever Bryce component you installed in the first place.

Did you install Bryce program first? You will need the following:

Bryce_7.1.0.109_Win32.exe, 253.76 MB. <------ Install first in the Program Files (x86) folder (the 32-bit applications folder) This is the pro and standard version. Serial number entered will activate the pro version of Bryce.

BryceProContent_7.0.0.19_Win.exe, 17,639 megabytes You add after you have installed BryceContent_7.0.0.21_Win.exe 670.03 MB This adds additional content for use with the pro version.

HTH?