Hello, I have some questions related to filters and the settings to use in camera. 
First question: filters are a must have? Some users say to use them always, others to use them sometimes and others to never use them on drones. What do you think about it?
To my understanding the main usage in drones is to obtain motion blur and stick to the 180° rule and to reduce the amount of light hitting the sensor ND filters are needed. With FPV there are two issues: to have a consistent exposure is not a good idea to use manual settings because you are continually changing direction and if you follow 180° rule and then you use EIS or apply stabilization with Gyroflow the footage will probably be crap and even Gyroflow documentation suggests to stick to 90° or 45° shutter angles. Do you use full Auto settings? Or do you manually set the shutter and use Auto ISO or the other way around? For example I've seen a Joshua Bardwell video about this topic and he uses fixed iso and Auto shutter + an ND filter if needed. What settings do you use? Are filters really necessary in your opinion?

It will depend on the look you want in your footage. As you noted the main purpose is to allow you to reduce shutter speed and introduce motion blur. These tiny cameras have fixed aperature, so the only ways it can adjust exposure is by shutter speed and ISO or sensitivity. In very bright light, at minimum ISO (usually 100) you will likely need a very fast shutter speed (way above the 180 rule - probably 1/800s or higher) which will result in a very crisp frame with no motion blur. When played back at something llke 30 or 25fps, it will look choppy, not cinematic/film like or disturbing to some, but others may like such a look of seeing everything sharper. It will also depend on the FOV of your lens, if you have an ultra wide and render at 60fps, the look maybe more acceptable.

Some additional advantage of ND filters are that it adds a layer or physical protection to the lens, if you camera is prone to jello the slower shutter speed will hide that.
Disadvantages, extra cost, extra gear to bring along, if you are picky in color it may add some color shift, may add extra flare when pointing at the sun.

In terms of exposure, if you are capturing a very specific scene, you could set all fixed exposures and fly your line. If you are going into and then out of the sun, then reset the exposure and fly it back the other way, but that is a pain. If you don't mind some exposure fluctuation in your footage, then auto is much more convenient. If you are using a Gopro, you can fix the shutter using 180 rule is you like that look, then set ISO to auto and gopro allows you to set max ISO so it won't get too grainy. This will result in some underexposed scenes, but with the lower ISO you can usually lift it back in post.

However if your plan is to use Gyroflow, then depending on your lens FOV as well, you may not want any motion blur and use a faster shutter. You can always add back motion blur after stabilization if you video editor has that effect.

I have a bunch of ND filters, and would use them in super bright sunlight, but I end up leaving them at home, and usually choose to fly sunrise/sunsets or partly cloudly days.

On this morning, the sun was a lot brighter than I expected and I wished I hadn't forgetten my nd filters. I had a Thumb Pro but the amount of jello was terrible, the GoPro footage was ok though. Probably not the best choice rendering at 30fps but maybe because of the slower flat flying, I think the high shutter speed actually didn't look too bad. https://youtu.be/3nRxoXnmxbU?si=y8_xevMG3I3YjKzE

Roughly which shutter speed was used without filter?

I had it set on auto shutter, but I am guessing under that sun it was close to maxing out the Hero 8 shutter speed so 1/480 or 1/960s.
For more distant landscape/scenery I think it looks fine, but if you focus on the corn/grass in the closer shots, then that sharp motion can be a little disturbing. And sorry it was rendered at 60fps matching to the original footage, if you are looking to render in 24/30 fps then the high shutter speeds would probably be much more noticable creating a stronger stop-motion effect.

Same camera/drone on a partly cloudy day and this time with a ND filter. Not sure why I recorded in 30fps instead of 60fps here, maybe because I wanted 4k footage. Probably could have used a darker ND filter, the motion blur kind of falls short, but I think that is personal preference too.
https://youtu.be/nz8Ellm5ReA?si=mx8vmkCSlSOw33fh