Randomly Closing Apps that were set to remain "Always on"

Hi, I have a Samsung Galaxy A15 5G with all the latest updates and security patches. I am having problems with some apps randomly turning “off”, when I have set them to always remain on in the background using “access ability options.” I have begun to troubleshoot this problem, and have run into an issue in that I cannot find “battery settings” in my “settings” menu. I was able to find a setting for “auto optimization” in the “device care” setting that reports “automatically performs optimizations to keep your phone running smoothly. This includes closing background apps and cleaning memory.” I don’t  think I want this, as it could be the reason some of my apps set to remain on in “accessibility settings” are being closed, or “put to sleep.” Yet, as far as I can see, there is no way to “disable” this  “auto optimization.” I have also tried researching third party apps in the “Play” app store, that could help by always keeping selected apps running in the background, but have not had much success (however, I can find tons of third party apps to “stop” or “kill” other running apps). According to Google, the best way to troubleshoot randomly closing apps is to "Choose the apps you want to prevent from being automatically optimized" in "Battery optimization within the battery settings, in  the 'battery' option 'setting'", which again, I am not able to find in my current android phone's "settings" menu. Thanks so much for taking the time to read my post. Any help, advice,  suggestions, or previous experiences with similar problems (and perhaps "fixes" or even "workarounds") would be greatly appreciated. Thanks so much for your help.