Hey there (23M). So I'm in the software development business for 3 years after getting my graduation on the same area spanning 7 years of my life. To make the introduction short, I'm working in the field I love, with co-workers that I knew from my last job (past year's lay-offs and whatnot) and with a supportive and fun work environment most of the time. I'm in the small group of colleagues that is still on remote. On a small team of backend devs, I ended up becoming the 2nd person with the most responsibilities and implementations one can get and, sadly, I'm very team oriented and like the management side of things. Why did I say "sadly"? Well:

Not shining the light on the 1st/2nd person "podium" conversation (because that isn't even a useful thought and will only be considered here to reference the co-worker), the fact is that the 1st backend person progressively makes the work environment toxic with small intentional attitudes and phrasings, resulting in heated arguments between us and sometimes between said co-worker and the rest of the team.

This back and forth has been going for months, and it is rapidly degrading my mental health and always increasing my stress levels when the time comes to interact with such co-worked. I regularly feel under judgemental supervision and controlled, in a sense that I must exercise double/triple caution for everything I do or say.

Upper management stances:

Tech lead ends up resolving some situations, putting them under the rug on other occasions, but most of all has been helpful and, with all the caution, I openly told them I'm using them to veto the quality of my work before putting it under review

Project/Team manager: Dismisses the situations with the usual pep-talk and teamwork speech but, since it is always in the office and the problematic co-worked is there too, with a loud and open opinion, I feel my side of the "story" ends up on deaf ears

What should I do?

(thanks for keeping with me after this long post)