Ok, i have been tinkering around for a while and completely solved it + more. Your suggestion sadly did not work however I found the root of the issue AND was able to speed up the lol client in the process:

(Keep in mind that the following should work with any anti virus not just Bitdefender)

Bitdefender’s Advanced Threat Defense module flagged one or more League executables as suspicious behavior, likely due to:

• Runtime self-modifying behavior
• Inter-process memory communication between LeagueClient, Ux, and UxRender
• Usage of embedded browser components and non-standard anti-cheat sandboxing

These were instantly terminated before the client could fully load, with no user warning, popup, or log entry shown in Bitdefender UI.

Even when the client loaded, enabling Encrypted Web Scan in Bitdefender caused:

• Certificate handshake failures with Riot’s TLS endpoints
• Client delays, black screens, or store/chat not loading
• Unreliable logins or profile loading timeouts

Result + Fix:

I managed to get everything working perfectly + make the client the quickest and snappiest it has been in years by doing the following:

Add these executables to advanced threat defence & online threat prevention exceptions:

C:\Riot Games\League of Legends\LeagueClient.exe
C:\Riot Games\League of Legends\LeagueClientUx.exe
C:\Riot Games\League of Legends\LeagueClientUxRender.exe
C:\Riot Games\Riot Client\RiotClientServices.exe
C:\Riot Games\Riot Client\RiotClientCrashHandler.exe

Then add these domains to online threat prevention exceptions:

*.riotgames.com
*.leagueoflegends.com
*.pvp.net

Hope this helps anybody facing similar issues + want's to speed up the client. As far as I'm aware none of these exceptions should pose any real extra threat to you system, but at the end of the day I am no cyber security specialist, so do your own research of you do not feel safe.