My name is Fenris!

I have been trying with this little guy for over a year. He seemed to be getting better, but I had an injury so wasn’t able to get out much for a few months, and I’ve been trying again, but his reactivity has escalated, and now he is more aggressive towards the smaller, older dog and the situation is frightening me.
Fenris is a 3 year old chihuahua mix. He weighs about 11#. He is occasionally calm and sweet at home, but at times gets anxious for reasons unknown to me. He is nippy at times, but will play with me nicely at home and sit next to me, but gets aggressive with other people and dogs, and sometimes with me. I have tried quite a few different online training courses and give him various CBD treats and oil. He likes toys and treats. I had him evaluated for group classes but he isn’t appropriate. I think he might do better with a male or maybe a couple, as I’m guessing his abuser may have been female. He does ok on a leash, but we mostly do loose leash in the yard.