How do I stop Elements 2020 from opening JPG in Camera Raw

If the jpeg files opens in ACR, it's because it has already been opened and saved in ACR in Elements (or PS or in LR). This is the expected behaviour by those who much prefer to use the 'edit in ACR' process;  the advantage in that case is that the organizer opens the file automatically in ACR.

If you want to open that file in the normal pixel editor, one option is to open the file in any other editor available on your computer and save them as copies or overwrite them.

I would rather recommend letting the file open in the ACR dialog. You have the choice to keep the settings precedently applied to the files or return to the original state without edits. Then, from the pixel editor, save in version set with the original.

You have the choice later to use either version. If you only want the original version, flatten the version set.