What I did is try to use the cipher :
ssh -c aes256-gcm@openssh.com (host)
If you get "no cipher found", you're clear, if you can connect you can disable the cipher (while keeping others) with this line in you sshd_config:
Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc