I'm no fan of Biden (though I did and will vote for him) but that's not what happened. He did not bust the unions, the 12 unions still exist. He broke a strike, which is the intended purpose of the Railway Labor Act of 1926.

The law he put before congress to force a resolution to the three year negotiation deadlock would have guaranteed the workers 7 days of sick leave per year (they wanted 15). It passed the House but the Senate knocked it down to 1 day, with a 14% immediate pay increase and an additional 25% over the next five years.

Biden continued negotiate for the unions to get the sick days. They don't all have them yet, but at this point 61% of the workers do have 4 short notice paid sick days with the option to trade three personal days for an additional 3 short notice sick days. Negotiations are still happening, the Biden administration is still part of them.

The Ohio derailment disaster was not a result of worker error (or lack of sick days) but lack of maintenance regulations, which was not something that was being negotiated at that time.

https://en.wikipedia.org/wiki/2022_United_States_railroad_labor_dispute

https://www.reuters.com/business/white-house-renews-pressure-railroads-over-paid-sick-leave-2023-02-09/

https://www.reuters.com/world/us/most-unionized-us-rail-workers-now-have-new-sick-leave-2023-06-05/#:~:text=Under%20the%20agreement%20effective%20Aug,use%20as%20paid%20sick%20time.&text=Our%20Standards%3A%20The%20Thomson%20Reuters%20Trust%20Principles

Beau of the Fifth Column, Let's Talk About Biden, the Rails and Sick days... Youtube link