Humans have caused 1.5 °C of long-term global warming according to new estimates

That is not how money and "work" functions. There is no way to "spend money" without spending energy and emitting CO2.

Assuming there is validity to the numbers (and no new source of energy), it means you need to reduce GDP by 2-5% yearly until 2050. But GDP and money is a "sliding" scale so it might mean something different by next year.

What are you talking about? If you take 2.5% to spend it on better infrastructure and existing technologies (that are more environmentally friendly) and develop new technologies, you are not reducing GDP. GDP just measures the ammount of money a country spends.

Of course you need to spend money and energy (specially energy, everything in the universe is energy), but the solution is not to stop moving. We need to use energy and resources in order to switch to better technologies.

The CO2 intensity of any activity can be vastly different. Net-Zero goals require that you transition to activities which produce less CO2. This can be negative CO2 emmissions (e.g. planting trees/felling them/storing the wood).

Replacing high CO2 intensity activities (burning coal) with lesser intensive tasks (e.g. burning gas or renewables) is the key.

Solar and other renewables counteract their Co2 expenditure after 1-2 years.

A new energy source is not like a new technology that can be developed. It needs to be discovered - as in a scientific break-through. A plan can not assume that break-throughs occur.

GDP measures the total production of an economy. That is mostly equivalent to energy_consumption * p_efficiency.

Investing in new technologies that increase efficiency has always been a good decision. Maybe you can improve solar panels by a further 5% and batteries by 10%?

Realistically, energy_consumption will need to decrease, but that isn't actually that terrible.

The amount of CO2 yet to be released depends on the amount of fossil fuel yet to be extracted. Current oil discoveries, wells, and coal mines will all be exploited as long as they are profitable.

It will be necessary to lower demand for fossil fuel enough that new prospecting becomes unprofitable. This will happen eventually due to the physics of oil drilling.

If you consider the amount of energy contributed to the world economy from fossil fuels, there is no clear path how to market alternatives in quantities that can make fossil fuels obsolete.

A more realistic scenario for around 2050 is that coal-power increases while oil for personal transportation is replaced by batteries due to high oil price.

No. The energy consumption does not need to decrease, the source must be more eficient. We have nuclear energy, despite the propaganda, nuclear energy (specially the Thorium reactors) produce very little waste and pollute less than fosil fuels or even solar panels. You do not need to discover a new source of energy to stop climate change. The problem is that people keep thinking in how much it will cost.

Again, GDP measures how much money is spent within a country, if there are several intermediaries in a supply chain, the cost of products and services increases and the GDP tends to rise.

If a country change direction and leans towards nuclear energy, the GDP (that is in fact a terrible measure) will increase cause the new expenditures.