Question formatFloat returns empty string

I didn't notice from which version exactly, but after 6.3 the formatFloat('0.000000', 5.1) function (for example) returns an empty string.
one more - sqldb finally stopped working with interbase/firebird. problems are many. starting from the unloading of dynamic libraries (which is called, but does not really pass).
all listed glitches are collected on ubuntu 20.
sorry

я не заметил с какой версии точно, но после 6.3 функция formatFloat('0.000000', 5.1) (например) возвращает пустую строку.
и шоп два раза не вставать - sqldb окончательно перестала работать с interbase/firebird. проблем - масса. начиная от выгрузки динамических библиотек (которая вызывается, но реально не проходит).
все перечисленные глюки собраны на ubuntu 20.

I'm pretty sure all the problems come from the "glibc" version.
is it possible to rebuild fpc compiler with old version of libraries? in my opinion, this would be the most correct solution, since it is often necessary to use one version of the development environment on several platforms.
P.S. I'm currently using version 6.3 because you switched to glibc-2.34 as of 2020 and the new versions of the IDE don't work properly.
P.P.S. I understand and appreciate your desire to use the latest versions of libraries, but let's be realistic - platform developers are bound by reliability requirements and they are least interested in a small segment of the Pascal development market