No, there are no such obligations at all. Every lawyer who has looked at this reached the same conclusion.
The treaties are very clear. Two years after invoking Article 50 all rights and obligations terminate.
Pensions are obligations of the EU itself, not the UK. The fact that the EU has failed to invest properly into a pension fund and is structuring its pensions as a ponzi scheme is not the problem of former members.
"The billions are not arbitrary, but to settle obligations arising from the UKs past membership, such as pensions for their EU personell."
No UK monkey was ever able to understand this. "Just walking away will make this obligations disappear". And "paying them is the fee that we get all the EU rights with no obligations".
You obviously know that and are pretending to be ignorant, considering it was all over the news at the times.