I found an option to enable in the web server for "high trafic sites", that may help in some cases, we'll see if it improves (not a magical thing, but many small improvements together can help).
This morning I see that Bytespider is a very active bot. They "attack" the site from multiple IPs (to improve their performance, to the detriment of the sites), and it is handled very stupidly since the different IPs sometimes retrieve the same thing

edit: that bot is especially stupid, I caught it looping through the makes page because it can't properly handle the "/" in some make names - there is a bug in their code, it works fine in all browsers.
I had to add a special rule to block the invalid URLs it was trying to request. Maybe I should just block that bot

Though that others are not much better, e.g. this URL that OpenAI (ChatGPT) tried to request:
vehicles.php?make=ram_model-c/vehicles_make-ram&model=c/movie_14403178-beef&l=de
I wonder where they find such mess
Same kind for the Bing bot:
vehicles_make-uralvagonzavod_model-t-34/movie_165537-Wei-xian-ren-wu.html
Are they all flawed? What a waste of internet bandwidth if it happens everywhere...