Bedbugs do exist, and they are not rare on the Caminos. How much of a problem they are to you depends on your reaction to them.
Some people do not react to bites at all. Those are the people that will claim that the bed bug problem ist exagerrated and that they are very rare.
Some people have mild reactions (like small flea bites / mosquito bites). For those people they are annoying but no big problem. If you've been bitten, put all (!) your gear into a dryer for at least 30min on hot temperature, or wash at least at 60°C and dry then, to make sure you don't carry them somewhere else. They die at high temperature.
Some people have severe allergic reactions. In that case, you might need medical attention if bitten. If that's the case, you certainly want to make sure not to get bitten. Check beds and mattresses thouroughly. Use a sleeping bag or liner and try to cover yourself at night (they don't bitte through fabric). Put your "night gear" (sleeping bag/liner and pyjamas) in a waterproof dry bag seperate from all your other stuff. So if you get them into your sleeping gear they don't spread into the rest of your backpack. Also put your whole sleeping bag into a large garbage bag or dry bag at night, and far away from the beds, so that they don't crawl in and travel with you to the next place. Put your backpack and the drybag with your night stuff into the hot sun whenever possible as precaution.
I do have bad reactions to them. So I know what to look for, how to avoid them and how to deal with them... and still got bitten almost every time I walked.
They are stuff made from nightmares for me. Took me four years to unpack my things from the 2017 Camino (was packed airtight since then). They die after 1-2 years without a meal. I also put everything I carried in 2019 into a garbage can in Santiago and bought new clothes for travelling home. That's how paranoid I've become.
Bedbug ptsd
But I still walk. It's all worth it.
Hopefully you're one of those people who don't notice them. Good luck and a bedbug free Camino!