As a (temporary) technician of voting computers, I can assure you that you should not worry here.
Each polling station has a computer for the president (as freaxje will try), this can only be started by inserting 2 pen drives (which the president received in a sealed envelope the day before). These pen drives are in the form of a trapeze, so you can not simply connect each usb stick here. This computer will not start if the thumb drives are not identical. Once the chair computer has started, 1 USB stick can be removed (if all 2 USBs are removed, the system will fail).
The USB stick that was removed can be inserted into a voting computer (3 to 7 per polling station). The voting computer needs this pendrive. Once the voting computer has started, the USB stick can be removed again, after which it can be used to start the next voting computer. Once initiated, the back of the voting computer is locked and then sealed (with a zippered tie).
This may seem a little inappropriate for some people, but the only thing a voting computer does is print a QR code on paper, which is then scanned. There is no physical connection between the voting computer and the chair computer (where votes are kept in the office). The chair computer also has no network connections. Once the QR code has been scanned, it will be placed in a sealed (and sealed) box. If something happens to the 2 USB thumb drives (where votes are stored), votes can still be retrieved on paper.
For people who do not trust this system there is also a voting computer with a handheld scanner where people can scan their own voice to make sure that the QR code printed is definitely their vote.
We can also take a closer look at the attack surface of this system:
Voting Computer: The data on the voting computer is only loaded when the computer is started through a USB device. Nothing in the vote itself is saved. To significantly influence elections through a voting computer, you must be physically present in the device. As we are already talking directly from tens of thousands of computer voters, you can not significantly influence the outcome of a national election (not even with an organized group of 100 people).
The chair computer really can not be done much since it also contains no data, and is constantly overseen by the president / co-chair.
There are 2 pen drives for redundancy and security, to do something with this you should be able to manipulate both before they end up in the hands of a president. As president, of course you could manipulate the thumb drives, but in a national election where you can handle 1000 votes out of a total of about 8 million votes is not very useful. Voices can also be rewritten on paper.
If you want to significantly influence the election, you can only do this as an employee of the company that developed (and operates) voting computers. However, I expect very strict controls and code revisions have been made here.
Voting through this voting computer system is at least as safe as voting on paper (which by the way is not perfect either). The only major disadvantage / advantage is that it is not possible to vote invalid (blank), while this is possible on paper.