First off you should have some experience with Diablo 2 Resurrected aka d2r and have a class build in mind. To find some great builds visit maxroll.gg in the Diablo 2 area. This link takes you to a ‘Hero Editor’ for the single player offline mode of d2r, with it you can setup a character with all the levels, gear, skills, attributes, way points discovered, quest completion, and more you might want.
I was wanting to try a lightning sorcerer so I made a level 99 with the absolute best gear, I didn’t fully min max every little stat (you can edit gear btw) but got most of it with perfect rolls to affixes. When I tried this the first time I did not set my skills and attributes up since it’s easy to do in the game. After you have created something you will then save a couple files that you can then download and then place into your ‘Saved Games’ folder, look up the exact location for this to make it all work.
Now when you next start up Diablo 2 R you should see a new character, note it may show it as being a level 1 character the first time you load it up. I had another small bug where my Inventory shortcut of the default ‘I’ key was somehow set as ‘E’, might be bugs FYI.
A tip is once you have played and setup the character more you can save the files it creates in the ‘Saved Games’ folder again to backup a more complete setup. Most people will backup the offline game files just in case. Another thing is this can also be used to stock up on things like the Stone of Jordan rings to spawn Dclone.