Firstly there is no Lubuntu 19, as Lubuntu is a desktop release and uses the yy.mm release format; having more than a single release per year (as do server releases). Ubuntu has specialist snap based releases that do use yy, but Lubuntu uses debs as it’s base packaging system as all yy.mm releases do.
It sounds like you’re talking about screen tearing, which if I’m right, will require knowledge of your video hardware at a minimum. It relates to the kernel module (driver) used by the linux kernel, and my goto command to get this detail is sudo lshw -C video (list hardware of class video) You can find the kernel module in use looking for the “driver=”.
Once this is known you have clues to find the configuration file, where a ‘tear’ flag may be set to fix the issue, or other options explored. I’ll provide another ~recent query related to tearing on this site for clues as to what I’m thinking. (it may not relate exactly unless you have the same hardware, but with module details you’ll know what to look for).