Check spelling might be popping up due to a few different reasons. If you're typing in the same document more than once, your computer may be trying to alert you to typos and errors you may have missed the first time. When typing in a browser, this may be because of auto-completion and auto-correct suggestions, which are often right but not always perfect. If you're typing in an application, it's possible that the spell-check feature has been set to alert you to any potential typos.
If you don't want to be alerted to typos, you can generally turn off spell-check in the program or app you're using by going to the "Options" or "Preferences" menu. Keep in mind that the menus may be slightly different depending on your computer or device. If the issue is due to auto-correction, you can try to disable this by going to your device's settings. There should be an option where you can disable auto-correction.
