Searching for an alternate vpn/ipsec client

Hello all,

i’am searching for an alternate vpn/ipsec client for Android that has als an encryption higher the AES128/SHA1 (Forticlient)
There are many on the market, can you recommend one that works well with IPSEC?
I already had the native Android client running a few weeks ago. I can’t tell you the level of encryption, you can’t set anything on the client. I had only been able to get L2TP to work. Unfortunately, surfing via the VPN was not possible via the Fortigate when the VPN was active. Unfortunately, the support team did not find a solution either.

Can anyone recommend a client for me? If possible OpenSource.
Very Thanks and Best Regards