Problems importing an SSH key

[kasoshadow]

I created an SSH key pair some time ago. I want to import it, however, I always get only different error messages: "Unsupported Algorithmen" "Invalid public Key"
To create the key file I had used kittygen (Kitty is a fork of Putty) with ED25519: https://drive.google.com/drive/folde...ThaTE92RmlodkE

Currently I have only two files: a ppk file and an SSH2 public-key file.

Now I go inside of FlashFXP to Sites -> Key-manager -> Import -> RSA / DSA / ECDSA key for SFTP. There I use the pkk as private-key file and give the appropriate password. The SSH2-public-key turn as a public key. When I try to import, the error message "Invalid Public Key" is output. If I leave the public-key field blank, the error message "Unsupported Algorithm" is output.
However, in FlashFXP Help file, "OpenSSH SSH-2" and "PuTTY SSH2" are listed as supported. However, I have neither a * .cer file nor a * .key file. I tried with kittygen and various export formats to import public-key and private-key, but this did not help.

Below is the schema of the two files.

---- BEGIN SSH2 PUBLIC KEY ----
Comment: "ed25519-key-20161216"
AAAAC3Nza****w6lk6h
ghoy
---- END SSH2 PUBLIC KEY ----

PuTTY-User-Key-File-2: ssh-ed25519
Encryption: aes256-cbc
Comment: ed25519-key-20161216
Public-Lines: 2
AAAAC3Nza****w6lk6h
ghoy
Private-Lines: 1
EfPOkHREfK***GfKxyGv/QLm4+z
Private-MAC: ea8c38dec***f08554abdf1

I would be very grateful if you could help me.