It is not possible to do harm with Reiki. The very nature of that energy is purely benevolent.
Can people do harm with energies other than Reiki? Yes. That’s what curses, hexes, jinxes, evil eyes, etc. are all about.
Do those people need to be physically present with you in order to do this? No. They can be across the globe as they do this. They’re not necessarily using the Internet, although they may learn if your existence through your participation on the Internet (like your example of leaving a review on the Internet). And they don’t need any “rational” reasons for doing so. (I know of certain witches who will curse their clients so that their clients will keep paying them.) That’s why @Maoshan_Wanderer cautioned us tobe careful about which energy workers (and sub makers and field creators and YouTube/TikTok videos, etc.) we’re using.
Now, the best way to protect yourself is to heal and build up your energy field. (A lot of these people are way less powerful than they imagine. The really good ones are usually directing their talents to building up their lives (rather than tearing yours down).
You have fields to clear your energy systems; to break curses; to remove cords and an
infestations; to build up quite a number of the different parts of your energy system; and to raise your vibration; and to protect you. You have Ultimate Reiki - Star Exercise Meditation (which, if you aren’t doing twice daily, you “should”–as much as I hate shoulding all over someone else). This doesn’t need to be as scary as you may be making it.