Servers are lagging

I keep getting high PL for no reason. It only happens when I spawn or when I’m about to dogfight, otherwise it never happens. Even if I only spectate the entire match, no lag. I spawn, lag. I see someone, lag. I die, no lag.
I’m being told time after time that the problem is on my side and it’s impossible it is, WT is the ONLY thing lagging and I even had some matches were people were just crashing, that can’t be my fault too.
I did a ton of speed test, optimised my routers settings, updated drivers, optimised settings on my PC… but still WT is the only thing laggin. No other games, not downloads, videos… I can watch videos while downloading stuff and whatever game is running doesn’t have ANY lag issues.
People told me it was my ISP, but I’ve changed, not only ISP, but also physical location over 200km away from the previous one and even hardware, with freshly installed Windows as well. It’s 100% impossible it’s my problem and I’m tired of being gaslighted for that.

Moreover, over two years ago, an admin told me to test the connection with the server but my question is: what’s the difference? Nothing changed from game to external testing, I can’t solve or test anything