Betta tumor(?) gotten worse and fin rot returning. Advice needed

My betta has been struggling with fin rot that begins as holes in the fins, then grow to larger splits, since around August. I’ve treated him several times with 3 different antibiotic medications. Tank parameters are monitored, tank is 10 gallon heated and filtered with live plants, and he gets weekly water changes. Maracyn II seemed to stop the progression of the holes and rot for a while, but there was very little to no new growth after stopping the meds. He’s been getting Indian almond leaves and vitachem since stopping the meds. He’s been pretty consistent for a month or two, not really getting better or worse, but this week a new hole has appeared for the first time in a while. He doesn’t seem to be able to fight the infection on his own. New growth only shows while he is still on the meds, and shortly after stopping it disappears. This is the second time he’s regressed and the holes have come back after stopping treatment. His dorsal fin seems to have shrunk as well.
He also has a lump just behind his pectoral fins that is a few months old. It has grown over time and changed color from white to blue. This week, it appears to have opened or turned into a wound. I’m honestly not sure, but it doesn’t look good.
I’m very conflicted about what to do. He’s still very active, curious, and eating, but it’s been really hard watching his body decline. It doesn’t seem worth it to continue to medicate for the fin rot since it only slows it temporarily. The tumor, cyst, lesion, whatever it is just seems to be getting worse over time. I’m considering euthanasia before it gets really bad and it starts to be painful for him, but I’m unsure. What would you guys do?
Do we think this is myco? I thought once symptoms of myco showed up it progressed pretty quickly, but I’m not super familiar. I’m considering completely disinfecting my tank just to be safe.

I'm not sure, but it looks like it could be lymphocystis. It's a virus, there is no treatment. Sometimes it goes away, but can come back. It doesn't look like mycobacteria to me.

Since he doesn't seem to be in pain or suffering, I would wait on euthanasia. That's always a hard choice. If he's eating well, I'd let him live a while longer. Keep up with water changes.

My fingers are crossed for your betta. Let us know how he's doing going forward. Maybe others will have more suggestions. Good luck!

Drug resistant bacteria causes the holes in fins that can't be treated and don't heal. It's becoming more common in male guppies and Bettas.

Mycobacteria usually affects internal organs and causes one or more organs to break down. The fish act normally until the bacteria destroy or does enough damage to an organ to cause organ failure. Then the fish stops eating, swells up overnight, usually does a stringy white poop, breathes heavily at the surface or near a filter outlet, and dies within 24-48 hours of these symptoms appearing.

Sometimes Mycobacteria will infect external parts of the body and these cause granulomas (small lumps) that are the same colour as the skin. There's no cure for Mycobacteria whether it's infected a fish internally or externally.

If the fish isn't responding to treatment it should be euthanised. You can do that now or wait a while, however if the fish stops eating, or has trouble swimming or remaining buoyant, then it should be euthanised immediately.

If there are no other fish in the tank, then disinfect it and all associated equipment after the fish is euthanised. If there are other fishes in the tank, then don't add anymore and let them live out their lives until they die. At which point disinfect the tank and equipment.

You can boil gravel and rocks for 10-15 minutes to sterilise them.

Plastic items can be bleached for an hour, then rinsed under tap water.

Live plants can be bleached but usually melt if left in bleach for too long. Most people throw the plants away and replace them.

The aquarium can be bleached for a short time and rinsed well. Then you can wash it out with white vinegar and leave that for a few hours before rinsing again. The silicon that holds the glass together can be broken down by bleach so only leave it in contact for 10-15 minutes before rinsing off. Silicon is unaffected by vinegar and that can be left on the glass and silicon for hours and will help kill anything left after a short bleach.

When using bleach, wear safety glasses and rubber gloves. Use bleach in a well ventilated area or outside in a shady spot.