No, there weren't 10,000 "objects" (defensive works) along the former Austrian borders. But a few hundreds were there. I thought there was not much there, myself, but I learned better here one of the last times this was brought up, by a Czech or Slovakian user.
If you are in a hurry, you can bike from Vienna to Bratislava in half a day, or in a day at a leisurely speed. However, the final approach to Bratislava from the easier, Southern shore of the river would have to cross Petržalka:
https://www.bunker.bs8.sk/zoznam-bunkrov/
Mind you, the Germans would have arrived in Bratislava anyway. But they would have had to go cross-country, through terrain not as easy - or they would have needed to reduce these bunkers.