Shout outs to SalmonBoiDab for letting me link to their saves!
Make sure to rate their nexus page as a thank you to them.

Here's a save file that has cleared the game, with this you can either start a brand new game on legendary difficulty, use the old file as a new game plus or use all of the unlocked options on the title screen, just as a note this isn't a 100% complete file. I have posted a guide like this for all the other Yakuza, Like A Dragon and Judgment games. Links to all of them can be found here and on my profile. The links can be found here and on my steam page:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2689025548
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2585769811
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2586740791
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2379715518
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2389968624
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2408950501
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2440359743
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2447367563
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2864943075
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2872921349

Amon fight save: https://www.nexusmods.com/yakuza0/mods/307?tab=description

After downloading the folder, unzip it, inside is a save called save0000.sav copy the save, go to where steam is installed and click steam, userdata, [your steam ID], 638970, remote and paste the save there. I recommend backing up your own saves, just incase. You might need to turn off steam cloud for Yakuza 0 for this to work, to do that, right click on Yakuza 0 in your library and go to properties and you will see a tickbox under steam cloud in general. For the Amon Kiryu and Majima have to take a taxi to the bull ring, the save is on legendary but can be turned down if you are having trouble, good luck kyoudais and again big thank you to SalmonBoiDab