There definitely an actively developped open source privacy focused period tracker available, go check it out: https://gitlab.com/bloodyhealth/drip But all data stays local on your device , which is of course good from privacy pov but if you are looking for something accessible from different devices then this might not be suitable.

I used to support testing the adblock solutions from Pixeltris some years ago when Twitch actively starting fighting adblockers. It turned out the only reliable way is to use a proxy or VPN of a country that doesnt serve ads via amazons ad system. Mostly small countries where it’s not worth place advertisments. I am using eithe czech, polish or Luxembourg IPs and usually dont get any ads this way anymore as there are no corporstions using their af service.