WhatsApp update erased the chat history. What has gone wrong and is there any way to restore it?

Seems like WhatsApp update has erased all my WhatsApp history. Is there any way to get it back? (Without paying for third party tools, if possible) I bought a new Android phone (Realme 7 Pro) and wanted to transfer my WhatsApp data from the old iPhone to the new Android phone. Seems like there is no way to do it easily so I had to buy a third party app that helped me to transfer the data. I connected both phones using USB, the app read WhatsApp messages from my old iPhone, then installed WhatsApp on my new Android phone and imported all the messages. After the successful migration I deleted WhatsApp on my old iPhone and all seemed to be fine. Then I was experiencing certain problems with WhatsApp and got a suggestion that I might need to update it. I then found WhatsApp in Play Store and there was a button reading "Install" on it. I got a bit surprised about why it says "Install" rather than "Update" but I thought that's just the way it is on Android. I then downloaded WhatsApp and got 2 WhatsApps on my desktop. I tried running the new one and it asked me to confirm the number. I then closed it and wanted to open the old one and realised that it was gone... I don't have backup of my WhatsApp history on iCloud either so I can't get it from there. I have previously backed up my iPhone using iTunes though so I might be able to get something from there, but still wondering what has gone wrong on my Android phone. How could WhatsApp installation just completely bin everything from the previous version?.. Thank you very much for any information/suggestions :)