I think the biggest thing that I haven't seen in another comment is that companies aren't being explicitly ageist, they just want cheaper labor and younger/less experienced people are willing to work for less money. I'm sure plenty of companies would be more than happy if you said "I have decades of experience but I'll take the salary of a junior position". Without something similar to a union or a change in laws to…
This is match my experiences. Saddly, bad middle manager wants to hire a yesman (or women). Not an experienced engineer that will challenge them by highlighting to upper management the project technical debt, the lack of tests or the broken CD pipeline.
Same. I've had interviews where people (younger than me) tell me "how do I know you won't be bored doing level-10 work, while your skills are clearly level-30 work? I don't want you to debate my budget or strategy" (because the team FTE costs is $2-3m and I'll be one of the pawns, while I've ran $20m teams as a rook or king).