The other thread I was referring to was this :Corrupt Filesystem every 2-3 months.
That’s an important point. In my case (a raspberry pi v3b) the original power supply is rated 2.5A but I have to use the 2.1A port of the power bank ( with a very short USB cable).
Three years ago I bough this powerbank: it delivers power either when it is being charged or not and there is no interruption during a power outage. This feature is not mentioned in the specifications and I’ve read somewhere that these powerbanks are not designed to work in this way. My raspberry can run up to 24h (at least when it was new, now probably less ): I can disconnect the powerbank from the original power supply and bring the raspi with me in a location where I can attach it to a screen.
Alternatively there are mini-UPS, still based on lithium batteries: I bought one like this for a 12V router: it should have also a 5V output, but I do not know it the rating is enough for Raspberry pi v4, which is more power hungry than the raspberry pi v3b. I sent it back as it was not able to power my fritzbox router (but it worked with a less power hungry access point).