Where did you "see" this?
Download links for Arduino IDE 1.8.19 are listed on the official "Software" page here:
https://www.arduino.cc/en/software#legacy-ide-18x
This includes the "Linux ARM" builds for use on the Raspberry Pi (make sure to use the 32-bit build if you are using a 32-bit distro on your RPi).
I don't understand what is the "it" you are referring to.
Generally using the nightly build is only recommended for beta testing. The exception would be if there was an impactful bug in the release version of the IDE that was fixed in the nightly.
Again, we need more information in order to be able to assist you.
If you downloaded the official "Linux ARM" build of Arduino IDE 1.8.19 from the "Software" page, you should definitely find an install.sh file in the extracted folder.
If you instead downloaded Arduino IDE 2.x, then there is no install.sh script in that package. But you should also be aware that there are no official Linux ARM builds of Arduino IDE 2.x so if you downloaded that IDE version from the "Software" page then it will never work on your Raspberry Pi anyway. Unofficial Linux ARM builds of Arduino IDE 2.x are available from some 3rd parties. If you are using one of those builds, then we need to know where you got it from.
Please provide a detailed description of what gave you that impression.
@Grumpy_Mike after so many years of providing support to the Arduino community, surely you should understand how to request support more effectively than you are doing here.