https://www.sightreadingfactory.com/
I have been trying to teach myself to sight read during these fun times of isolation and after having worked through a couple of the SBL Sight Reading courses I came across this site on their forums.
Genuinely the best thing I have found so far and my reading has come on loads in a short space of time through repetition. The site auto-generates 8 bars of music at a difficulty you can preset and then you can try reading it, playing it and then it can playback so you can play along with it as well. It was $35 for a years subscription but you can get about 18 pieces free to try it out. Would highly recommend it for those wanting to improve their reading.
Disclaimer: They have a referral service where you can get free months if people signup. I have found this genuinely useful so posted the link above without referral tag as it has genuinely improved my reading in a short space of time. I have posted my referral link below but don't want to appear like I am pushing the site for my own benefit.
https://www.sightreadingfactory.com/share/3bDdHL60vAmh6mxkPrC4