Well, since it's just a lightning wallet, I didn't put much on it and I'm not sure what I did with the seed (I know it's not right ...). So what I did, I just restarted the smartphone and the wallet opened again. I'm not sure what to do with this wallet now after that strange white screen.
I have a Redmi 12C (XIAOMI), in case anyone's interested I can also give the other technical specifications.
Good that you have access to the wallet but make sure you backup your seed phrase. That phone was released 3 years ago and probably it can not update to the latest Android. It would be good if you get a better phone. There are many cheap Android phone with 8 gigabyte RAM now and better processors, running the latest Android. Also phones of nowadays have many years OS upgrades.
=> I saw that phoenix wallet can show the seed (like trustwallet), this time I will write it down in case of a new "blackout".