No, in GTA 3 Definitive edition, there is no cheat for unlocking all islands in GTA 3, but you can cross the bridge by using this trick – click here to see.
In the new GTA 3 game, an old trick is now not working, I already tried my times but that trick is not working in the new GTA game but in the old GTA 3 that trick is working.
If you want to cross the bridge in old GTA 3, then it is possible by using this trick, click here to see
Definitely, many times, you will fail to jump to another side but after doing again and again – you will get success. This is a working trick in the old GTA 3, but don’t apply this trick in GTA 3 definitely edition because it will not work in GTA 3 Definitely edition.