Will my old Dell PC work with Migration Assistant on iMac?

this would not work Download Windows Migration Assistant v3.0.1.0 - Apple Support

this older one might Download Windows Migration Assistant v2.4.5.0 (Monterey and Ventura) - Apple Support

otherwise you can always copy stuff over manually (network or external storage drive/usb) though a lot more work

Another option to migrate from your Windows machine to the Mac is how I did it years ago when I made the switch. Simply copy the data files you want to an External Hard Disk and then once you have the Mac setup copy it over. This is an extremely simple approach and pretty trouble free. NOTE: One very nice thing about doing this is if you have a large library of photos on your PC. All you have to do is copy them (put them in 1 folder on the PC and select all of them) and drag them from the External Hard Disk to Photo's app icon (on the Mac's Dock) and all the photos will be copied and automatically imported into the Photo app so you can then organize, edit and manipulate them as you want. This approach is much easier than importing or any other method of organizing large photo libraries.

Transfer from PC to Mac with Migration Assistant - Apple Support says that you should "install the latest Windows updates" – but doesn't really spell out what happens if you don't.