I have changed this TLSProtocol TLSv1.2 TLSv1.3 on 17th line to TLSProtocol ALL -TLSv1.3 . Also, I tested your suggestion which works as well: TLSProtocol ALL -TLSv1 -TLSv1.1. This code fixed the following issue:
proftpd[147843]: fatal: TLSProtocol: unknown protocol: ‘TLSv1.3’ on line 17 of ‘/etc/proftpd/tls.conf’
But there was another issue. For some reason I found out that passive ports are set: PassivePorts 45000 65000 (proftpd.conf) which are wrong. I set them as:
PassivePorts 12000 12100 and now all works well. This issue is resolved. Thank you.