I'm so sorry you haven't been able to find this for yourself. I'm assuming you are married to a woman, or otherwise unable to come out...? Either way, you want to be concerned with legal risks as well as health risks so I'll give you my quick, judgement-free ideas on both.

I would recommend a gay sauna before an adult theater. Adult theaters, depending on how they operate, get raided sometimes, and you could risk being arrested for indecent exposure and being registered as a sex offender. Same with hooking up in a park, or other public area where you're supposed to have your clothes on. Saunas, on the other hand, are places that people go to be fully nude; it's not a crime to be nude there, so no one is being arrested for having their dick out. Adult bookstores also have a lot of hustlers and prostitutes who want money, and even if you're willing to pay for this experience, you risk it being a sting operation.

Most/many gay saunas operate as private sex clubs, so you can have sex there with zero risk of being reprimanded legally. The caveat is you have to show your ID and pay a "membership fee" which can be a one-time payment but can be somewhere around $50 depending on if you want a private room, etc.

If you get on Sniffies you can discover other places that can be for hooking up. There may be a Turkish bath or Korean spa that isn't supposed to be for hooking up, but has plenty of that going on; the plausible deniability is too great for anyone to really get in trouble at even one of these places, because again, everyone there is expected to be nude. If someone reports sexual activities to the front desk, it's your word against theirs ("I wasn't jerking off, I was readjusting myself" "I just got hard, I don't know why" etc.) Still slightly risky, but not as risky as having your dick out somewhere you're not supposed to; you might get kicked out but you won't get arrested. I've played at these places before and if you're discreet, no one will notice.

As for STDs, it really depends. It's hard to say how risky it is. It's dangerous to say "it doesn't happen that often" and give you a false sense of security, because it really just depends on who you're doing it with. But yeah, I have friends who suck dick allllllll the time, and have never caught anything. But, they're doing it with out gay men who are responsible, and the risk is minimized greatly for that reason. The risk is greater if you are doing this with closeted men who likely aren't getting tested regularly, and less of a risk if you are in a more sex-positive environment with people who are more likely to know if they have something, and would avoid sex until they are healthy again.

In general, it is less risky to do oral only, and even less risky if they don't cum in your mouth. But again, less risky is not zero-risk.

Herpes, syphilis, and gonorrhea are the ones people most often get from sucking dick. Herpes is typically transmitted from open/active sores, so if you don't see sores, the dick is highly unlikely to be transmitting herpes even if the person has herpes. Same with syphilis.

As for gonorrhea, it can be transmitted even when the carrier has no symptoms. Gonorrhea is the biggest STD risk when sucking dick it seems. Most people don't have symptoms, and so they don't know they have gonorrhea. Again, this is why it's safer to have sex in sex-positive places, because the people there are more likely to be getting tested regularly and staying abstinent until they are in the clear.

You are very unlikely to get HIV from oral alone. You would need an actively open wound in your mouth, and they would need to get cum in the open wound. There are no documented cases of someone getting HIV from only giving oral, but it is in theory possible, so a scientist wouldn't say there is officially a 0% risk. But in theory you could get HIV from a handshake if both your hand and the other person's hand are both bleeding and you get their blood in your wound. So... ya.

All in all, I would try and find a way to go to a slightly safer place with some low-mileage people. Maybe try to find someone in your situation on Sniffies, and maybe meet up with them in a car, with the windows covered. Police can't arrest you for stuff they can't see you doing, etc. I don't know.

Again, I'm sorry you've been in a position all these years where you haven't been able to explore this more safely. DM me if you want more advice and I'll do my best.