If you hit escape to go to the pause menu (the one where you can save, load, or quit) and then hover over one of the icons at the bottom, it will show your map and game seeds.
Then, you can go to create a new game, go into advanced, and enter your seeds. Note that they're backwards. That is, the pause menu shows one seed first, but the create game menu asks for the other seed first. Just make sure that game is game and map is map. Don't forget the negative sign (-) if there is one.
You'll have to make sure that the map size, type, and options are otherwise the same. You also need to select the same civs that you did before. If you had random AI civs before, then you don't need to select those. They'll random to the same ones as last time. The difficulty level doesn't matter, though. You can set that to whatever. I think that you can also set the disaster intensity to whatever you'd like, but I've never tried changing that for a reloaded map.
If you don't remember all of your settings, then go into the directory where your games are saved and copy your single-player save into the multi-player save directory. If you don't have a multi-player save directory, then create one called "multi" at the same level as "single". When you go to create a multi-player game, you can load the single-player save that you copied over and it will show you all of the options. It will also spoil the AI civs, if you haven't met them all, yet.
maybe there is some data, where placed civ6 maps with their numbers? Thanks