...available lighting can be extremely challenging as to colour balance more often There can be all kinds of mixed light- some daylight coming in through windows, some colour bu stained glass, old light bulb or fluorescent tubes, a mixture of new and old lamps, mercury or sodium lamps wit discontinous spectrums, LEDs and if yo are lucky one kind of light source that you can custom white balance for. The light may be uneven as well.

Problem is, if you are shooting a ceremony and need to capture the action, it is difficult to arrive at a custom white balance by testing and adjusting. It is unlikely that you will always be able to arrive at the correct colour balce without any post-processing. The automatic white balance shod get into the ballpark, enough to enable you to make the correction in post without too much trouble.

Even a pre-set for "tungsten lighting will yield warmer than normal colours because most interior light in churches is of a lower Kelvin temperature. My rule is, well it is a church, so only God knows what's in the lighting fixtures. If I have time, I can get in earlier and establish a white balance but it still may need to be tweaked in the post....

Personally, my experience is all digital cameras have great difficulty in these lighting situations. You asked how to do in the camera.

There are several tools that you use to either (a) capture a reference image for editing later or (b) create a custom WB in the camera. The reference image can be a grey card, something you can get as a credit card size you always have handy in your wallet. See WhiBal. You'd just stand under the light in the same position as the priest and take a close-up (frame filling) image of the WhiBal card under those lights. Then, use that reference image later in editing. Other tools cover the camera lens opening, and again, you photograph the scene and lights and then tell the camera to use that all white (yellow) image as the WB reference. See your camera manual for the process and a tool like the Vello Universal WB Handheld Disc.

Personally, I think your use of AUTO WB and editing in LR is the best and most efficient approach. As annotated below, pull the image into LR and use the WB 'eye dropper'. You can click around the image looking for something 'white'. Or, use the reference image from the WhiBal or Vello image. My older LR6 only gets 'close' where I still need to adjust even LR's thoughts on the proper WB. You need to assure you're working from a calibrated monitor.

As mentioned in earlier comments, shooting in RAW gives more finite control over the K temp and the Red-Green tint in your digital editor. You might also look at your flash usage. The EXIF shows and EOS 80D in 'normal' program, with a flash firing at 1/80sec, ISO-1600, f/5.6. I think you could have used different exposure parameters, outside of program, where you could manage an external Speedlite flash to output more light, with a smaller aperture, faster shutter and lower ISO-1600. That, all that is a bit more complicated where just updating the WB in Lightroom is easy enough.

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I would argue that mixed lighting is exactly when a Custom White Balance is most useful. If you will be standing in one place throughout the event and shooting one location where the light will be consistent, you can just set a single CWB. If you will be moving around and shooting from different directions so that the mix of lighting will change, you may need to do "sample shots" in advance from each planned location to be able to change the CWB as you go.

You also may need to take additional sample shots during the event to use for new CWBs, if the lighting mix will be changing during the event. For example, if part of the mix is sunlight coming in windows it will change as the day goes on the color of light will change, you won't be able to match it very closely with shots taken in advance and you'll need to update CWB periodically.

Another tactic is to put your neutral target right into a series of of test shots in advance of the event (one test shot from each location you'll be shooting, in the event of variable lighting)... then shoot RAW and just sample the target shots to set a CWB in post-processing. You may still need to tweak things a little.... but should be able to get much closer color rendition. Some people like to do these shots with both a neutral target (white, gray, black... doesn't matter so long as it's truly neutral)... As well as a MacBeth Color Checker panel. Those have a series of colors that can help you decide what tweaks are needed.

Whatever route you choose to take, get to the venue early so you have time to take the prep shots that will be used for CWB or post-processing.

P.S. This is one heck of a lot easier with digital than it ever was with film! To accomplish the same thing with film and get highly accurate colour rendition often involved a lot of advanced work.... everything from shooting test rolls of the film you'll be using (because how it renders colours varied from batch to batch), to changing out all the light bulbs and/or providing your own lighting, to carrying around a whole bunch of colour correction and colour conversion filters. It's soooooo much easier today, with digital!