We get these. It's usually nothing at all to worry about. You should have it looked at by your doctor though if it doesn't go away.
https://www.nhs.uk/common-health-questions/mens-health/what-is-this-lump-on-my-penis/ Peyronie's Disease is a lump on the shaft from scar tissue. It's fairly rare though. Have you had any recent sexual activity?
Your best bet is to get it checked out.
It may be syphilis. You should go get this checked out by your doctor. If it is syphilis, a couple of doses of penicillin should cure it.
I know the two most simple causes of such nodules - it can be a kind of scar formed after an injury (most often due to pinching of the skin on the penis with the zipper), and it can also be a mole. Even if you didn't notice it before, because it could have appeared recently. However, just in case, still show yourself to the urologist, to exclude something more serious.
So, strangely today it has reduced to about 1/5 the size it has been over the last couple weeks.. This happened once before and then it started getting larger again. It almost seems like it’s a build-up of something and then it breaks down, builds back up again.. Weird. Again, it’s completely painless and gets no bigger than a piece of rice. I have an appointment with a urologist in 8 weeks, but in the meantime I’m just baffled.
I would advise you to visit not only an urologist, but a dermatologist. Something similar to your problem according to the description, but on the skin of the back of the hand, once happened to me. I was prescribed some kind of ointment, but I don't remember which one. In any case, for such a delicate place, another drug is most likely needed. Let the doctor examine the penis, it is advisable to make a scraping of this formation to determine the treatment. Most likely, this is a kind of mycosis, they look very differently and there are many varieties of them.
Update: This hard nodule or lump completely disappeared about a week ago and has not reappeared. Weird..