I first got RA at 50 in my right shoulder making Tai Chi uncomfortable. I'm now 86. Information was scarce and the doctor gave me 3 options, pain killers, physical therapy, grin and bare it. I tried all the different supplements to no avail. I read somewhere that heat may help, heat level and duration time were not included. I had an old heating pad . So I put it on my shoulder , set it on high and put a large towel on top to keep heat in.  Then spent about 3 hours watching TV movies. The next day my shoulder was red but arthritis was gone, but by the end of the day the redness was also gone.
After that I started getting RA in most of my joints and experimented varying the two parameters. .There were stages of pain during the process.  First after many hours I found only the highest and second highest settings worked.
The pain initially was was intense around the joint and after a while dropped to a lower level. When the pain went down to just warm I let the lingering for equivalent pain time again.
Recently, because of COVID 19, I became interested in viruses and developed a simple treatment using heat to cause the virus demise. This led me back to how I stopped RA in which the temperatures were much higher but following the same rules with colds. This leads me to speculate that RA is virus related as the duration time for demise is similar.
Also, our body's reaction of causing heat at offending infected areas, to me is a clue.
Comparing the two situations of colds and AR I would say the arthritis viruses are more robust, first attacking the outside skin layer then slipping in through the synovial membrane to infect the joint.
But what do I know . I'm a mechanical engineer. Alan Robb PEng retired, PhD