Greece is the only euro area country to have ever had debt restructured, in 2012 and again in 2015. AFAIK the old bonds were exchanged for new ones with lower principal and/or longer maturity. I assume they trade normally.
Short answer, no. Long answer is it basically took a collective bailout to avoid Greece and a couple of other countries collapsing. You might remember one of them... Ireland!
Many Greek private bondholders did not get their full principal back on time. See here.
Also known as the PSI (private sector involvement) or private sector haircut, it was a restructuring of Greek debt held by private investors (mainly banks) in March 2012 to lighten Greece’s overall debt burden. About 97% of privately held Greek bonds (about €197 billion) took a 53.5% cut of the face value (principal) of the bond, corresponding to an approximately €107 billion reduction in Greece’s debt stock.
I believe trades on Trade Republic are performed on the Lang & Schwarz exchange. You can see the recent trades for the bonds you are interested in on the exchange website. When I last looked at the Irish government bonds on there they only had a few trades within the past few months, but perhaps others are more active.