My suspicion is it is Chromebooks primarily. My kids were all issued Chromebooks starting in middle school (U.S.) and there is no way a pubic school in the U.S. can afford $400 or more machines for each student. In our case the kids were issued $200 Chromebooks. Why, because they can be efficiently configured and maintained.
Used machines, yeah right. You obviously haven't carried one around much or tried to keep one working on battery for a few hours at a time. I've bought used ones and the first thing that has to be replaced is the battery, that'll be another $20. Installing ChromeOS or something that won't be easily corrupted ... hmm. Lock down machine to the school echo system, that will be $xx and this many hours of time. I think the public school system my kids are in had one band director handling the ID for middle school, and one dedicated person to oversee it all. The only option is seamless administration of the machines.
If you have skills, I am sure the schools would like your assistance. There are still some machines used for programming, cybersecurity and developer courses that require something more than ChromeOS. Those often are 8 years old and dire need of some love and maintenance.
As far as critics and teaching. I'm not a teacher, but saying the teachers want to get paid to not teach is just rude. From what I see they are doing their best to create curriculum and new ways to hold the students accountable for their lessons and also following up on progress and areas where students are struggling. My kids' teachers DO CARE and are doing the best they can under the on again off again politics of this year's Covid-19 education.