7zip (open any archive)
VLC (open any audio/video file)
IrfanView (+ the "all plugins" installer on the same page, open any picture file)
SumatraPDF (read PDFs)
Libreoffice (to open any office files)
NAPS2 (easy scan, and split/merge/... PDFs)
Ditto (give your clipboard a memory)
Everything (an instant file search that works)
TeraCopy (replace windows copy with queue, queues, add files to the queue instead of starting a second parallel copy, pause that works, ...)
Powertoys (so many to list ... mass rename file easily, screen ruler, text extractor ...)
If it's appropriate : Qbittorent (clean torrent client)
Nvidia graphic card ? NVCleaninstall, so you can install just the clean driver you need
Windows 10 or 11 ? O&O Shut Up (to disable all the telemetry and onedrive in one click, there are plenty alternatives but I sort of like this one)
Windows 11 ? ExplorerPatcher to remove suggestions in the start menu and the new and terrible castrated contextual menu
And of course your browser of choice and extensions
In ten minutes you have a computer that feels much more smart and usable. There are plenty of great software out there, but I feel like many what to install lists are very topical or include software you won't use in many cases or once every 6 months, so this is my short list of what you will use essentially every time you use the computer.