I use \usepackage[para]{threeparttable} as suggested here (https://tex.stackexchange.com/a/160113/231568) to try to display table footnotes in one line.
The size of the footnotes is controlled with \appto\TPTnoteSettings{\footnotesize}.
But the footnotes are not really displayed in one line as you can see in the following picture. There is e.g. still space after [a] and [c].
To display the notes in one line, I additionally tryed the command [flushleft].
% Preview source code
%% LyX 2.3.6 created this file. For more info, see http://www.lyx.org/.
%% Do not edit unless you really know what you are doing.
\documentclass[12pt,english]{article}
\renewcommand{\familydefault}{\sfdefault}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{geometry}
\geometry{verbose,tmargin=2.5cm,bmargin=2.5cm,lmargin=3cm,rmargin=2.5cm}
\setlength{\parskip}{\medskipamount}
\setlength{\parindent}{0pt}
\usepackage{array}
\usepackage{setspace}
\onehalfspacing
\makeatletter
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% LyX specific LaTeX commands.
%% Because html converters don't know tabularnewline
\providecommand{\tabularnewline}{\}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% User specified LaTeX commands.
\usepackage[para,flushleft]{threeparttable} % threeparttable: to support table footnote, but this does not work correctly, looks ugly and footnotes are not displayed with fontsize footnotesize
\usepackage{booktabs} % booktabs: to support centering of table
\usepackage{etoolbox} % to support footnotesize within table
\appto\TPTnoteSettings{\footnotesize} % footnote font size within table
\def\tnote#1{\protect\TPToverlap{\textsuperscript{[\TPTtagStyle{#1}]}}} % brackets in table footnotes
\makeatother
\usepackage{babel}
\begin{document}
\section{Section one}
\begin{table}[h]
\caption{Lorem ipsum.\label{tab:Lorem-ipsum.}}
\centering
\begin{threeparttable}
\begin{tabular}{>{\centering}m{1.2cm}>{\centering}m{3.5cm}>{\centering}m{2.5cm}>{\centering}m{2.5cm}>{\centering}m{2cm}}
\hline
\noalign{\vskip0.1cm}
\textbf{\footnotesize{}a\tnote{a}} & \textbf{\footnotesize{}b} & \textbf{\footnotesize{}c} & \textbf{\footnotesize{}d\tnote{b}} & \textbf{\footnotesize{}g}\tabularnewline[0.1cm]
\hline
\noalign{\vskip\doublerulesep}
\noalign{\vskip0.2cm}
\textbf{\footnotesize{}1\tnote{c}} & & & & {\footnotesize{}1\tnote{d}}{\footnotesize\par}
{\footnotesize{}2\tnote{d}}\tabularnewline[\doublerulesep]
\noalign{\vskip\doublerulesep}
\noalign{\vskip\doublerulesep}
\textbf{\footnotesize{}2\tnote{e}} & & & & {\footnotesize{}1\tnote{d}}{\footnotesize\par}
{\footnotesize{}2\tnote{d}}\tabularnewline[\doublerulesep]
\noalign{\vskip\doublerulesep}
\noalign{\vskip\doublerulesep}
\textbf{\footnotesize{}3\tnote{f}} & & & & {\footnotesize{}1\tnote{d}}\tabularnewline[\doublerulesep]
\noalign{\vskip\doublerulesep}
\noalign{\vskip\doublerulesep}
\textbf{\footnotesize{}4\tnote{e}} & & & & \tabularnewline[\doublerulesep]
\noalign{\vskip\doublerulesep}
\noalign{\vskip\doublerulesep}
\textbf{\footnotesize{}5} & & & & \tabularnewline[\doublerulesep]
\noalign{\vskip\doublerulesep}
\noalign{\vskip\doublerulesep}
\textbf{\footnotesize{}6\tnote{g}} & & & & {\footnotesize{}1\tnote{h}}\tabularnewline[\doublerulesep]
\noalign{\vskip\doublerulesep}
\noalign{\vskip\doublerulesep}
\textbf{\footnotesize{}7\tnote{i}} & & & & {\footnotesize{}1\tnote{h}}\tabularnewline[\doublerulesep]
\hline
\noalign{\vskip\doublerulesep}
\end{tabular}
\begin{tablenotes}
\item [a] Lorem 0.00 mmol sit amet, consetetur 0.00 mmol sed diam nonumy.
\item [b] Lorem ipsum dolor sit.
\item [c] Lorem 00 mol% sit amet, consetetur 00 h elitr.
\item [d] Lorem ipsum dolor sit amet.
\item [e] Lorem ipsum 00 mol% sit amet, consetetur 00 h elitr.
\item [f] Lorem dolor dolor sit amet.
\item [g] Lorem ipsum 00 mol% sit amet, consetetur sadipscing elitr.
\item [h] Lorem ipsum dolor.
\item [i] Lorem ipsum 00 mol% sit amet, consetetur lorem ipsum dolor 000h sadipscing elitr.
\end{tablenotes}
\end{threeparttable}
\end{table}
\end{document}
With this the notes are displayed better in one line, but the notes have standard text size and not footnote size anymore.
How can I correct this? Footnotes clean alligned in one line, with footnote size?
\footnotesizeright after\begin{tablenotes}. – Bernard Jan 11 '21 at 20:19\footnotesizeright after\begin{tablenotes}[flushleft]. But then I have again the issue which is displayed in my first picture. – wewa Jan 12 '21 at 18:27