The collapse of the GDR has many reasons, mostly it ran out of money during the 80s. There have been several reasons for running out of money, e.G. taking on massive credit in the 70s to produce more consumer goods and build flats (the reason Honecker was very popular after his coup against Ulbricht), which it had problems to pay back in the 80s. Also minor things like spending millions on importing coffee (all experiments to replace coffee with something else failed - Vietnam is one of the worlds biggest coffee exporters because of GDR investments that came too late).

Another reason was Russia cutting cheap oil during the 70s after the oil shock. The GDR had imported cheap oil from Russia, was refining it and selling it with high margins to the West for $/Deutsche Mark. That source of money dried up in the 80s.

With sparse resources, the GDR was between a rock and a hard place. For modern production it needed chips, reverse engineering western chips e.G. Z80s (reverse engineered chip called U880 in the GDR) or smuggling chips was very expensive (~5-10x the price). Building chips on their own was also expensive. But they decided to invest billions into home grown chip production (they smuggled a whole factory via Austria, see "Red Fini") leading to the famous 1mbit chip "U61000" - which was old at that time, also the Japanese produced the same amount of chips in a day that the GDR was able to produce in a year. So things went nowhere.

But those billions were not available for other things.

Without money ($, Deutsche Mark), in the 80s to pay back credits to western banks a lot of vegetables, fruits and consumer products like clothing and washing maschines were exported to the West (most of the fruit production of the GDR around West Berlin went to West Berlin, many products in the West German QUELLE catalogue - like Sears - were made in the GDR). These products were missing in local shops, shelves were often empty, especially outside the large cities like Berlin, Leipzig and Dresden.

Additionally factories in the 80s in the GDR were in a very bad state (my father in law was head of production in a large machine factory in East Berlin during that time), lots of stuff was being stolen on a constant basis, maschines were old and lacked computer support (see above). This again reduced available consumer goods.

Because consumer goods were scarce, when things were available people bought more than they needed, leading to more scarcity (as seen during the pandemic). It is said that every household in the GDR had a second car as spare parts (another example are agricultural factories hoarding harvester spare parts, so when broke down, spare parts where hard to get).

Missing consumer goods in the GDR led people to leave their jobs in factories whenever something was available, e.G. rain boots, which reduced productivity even more.

In the end so many things were missing that people mass fled the GDR when Hungary opened the border.

All this together made the Central Committee believe everything is lost (book to read in German "Das Ende der SED - Die letzten Tage des Zentralkomitees" with meeting notes from the Central Committee), and the Russians not willing to come to help with tanks this time [0] (like they did in 1953 to kill Germans to keep the communists in power in East Germany) power was transfered to the people leading to reunification.

[0] For comparison: When Poland went bancrupt in 1980/1981 Russia and the GDR were near an invasion - which Poland prevented with a military coup.