Edit: Found it!

Overlooked so hard. It was the green one over Farmlands

I have 1 missing and I'm going crazy revisiting every spot to no luck.

I've noticed the blue one at Mt. send it's not even there (?), maybe this is my last one.

Update: I don’t know if it can help but for me re-playing a couple of lone wolves made appear the thumbs on the last one (for me it was the pink track in farmlands). I’m pretty sure it had no thumbs before because I checked all the spawn locations with the photo mode.

I used photo mode to check every path and spawn location but I think the achievement is bugged. I beat every lone wolf but no achievement.

Thank you I realized I'm just colour blind and thought there were multiple colours of the particle effect. I can see that the completed ones have yellow flags. Thanks for your help :)

Re: How to recognize which wolves are completed:
The ones you haven't completed yet have a blue flag and the thumbs up particle effect. See the picture at the top. The ones you have completed don't have this effect and a different color flag.

Re: Unfortunate colors:
Yeah I see the issue, sorry it took you some time. The colors were assigned randomly by a computer program, and I don't have it lying around anymore. For future bikers: a contributer copied the spawn points to the wiki (thank you!), you can use that to keep track of your progress and which ones you haven't seen yet: https://wheel-world.fandom.com/wiki/Map:Wasteland .

This guide is fantastic but i have one small issue, namely i was sure that i was beat every single wolf on the map but for some reason the quest card showed that i had 2 more wolfs to beat, then after closer examination of the map i noticed that the two routes very close to each other are marked with the same colours and they make it look like it was one route, i would never have noticed it if there weren't any dots there. This two places are marked as pink roads in upper area on the second map and as green roads in the city.

I’m new to the game - is there any indication for if you've beaten a specific lone wolf, or no? There's a few that I think I've raced, and a couple have green thumbs vs blue thumbs behind them

Thanks!

You single handedly saved my hundo, im eternally greatful