Demise

Why not? B-2s can AOS assuming their period of admission is still valid and F2A is current (which it is). If he entered on a ESTA/VWP then yeah I'd agree with you because 245(c)(4) prohibits that for F2As. If he were to overstay before filing then 245(c)(2) would prevent adjustment as an F2A. I also don't smell any "entry on tourist visa with intent to adjust" here either because we wouldn't be having this thread of "hey, is this possible to do". So presuming he is still in valid B-2 they could file the whole AOS package (I-130, I-130A, I-485, I-765, I-131, I-864, and I-693) and adjust in US. Pending I-485 will put him into period of authorized stay while that's being processed, the only caveat is that he'll be unable to leave until at very least the I-131 for advance parole is approved. The important thing is that it gets to USCIS while his period of admission (as per his I-94 and/or admission stamp) is still valid. @TBoneTX care to explain what's up? I see @dwheels76 talk about an overstay but OP neither said that nor affirmed it. I don't see any other blocks, so what the ****?

Yeah I meant for an EB not for any work non-immigrant visa (H, L, O, etc). Yes it's possible, I-601A can be used for IR, F1-F4, EB1-EB5, and DV Lottery. In most cases the sponsor and the qualifying relative are one and the same (e.g. USC spouse or parent) but they don't have to. So being sponsored by an employer in lets say EB3 and using your LPR father as a qualifying relative for I-601A is a valid option.

Have father file I-130 for you as an F-2B (unmarried son or daughter over) wait for the priority date to become current (6+ years), pay for DS-260, file I-601A using your LPR father as your qualifying relative, have it approved, file DS-260, get your interview date, leave, attend your consular interview, get your immigrant visa, and come back. If you leave before then you will get a 10 year ban, in case of which the process is similar: wait for I-130 priority date to become current, file DS-260, get date for consular interview, show up, get denied, file I-601 using your father as a qualifying relative, wait for it to get approved, get another consular interview date, get your immigrant visa, come back. Only important thing here is that you don't remarry before your father naturalizes as that will kill the F2B petition. If you marry after he naturalizes that'll drop you down to F3. Alternatively if you can find an employer to sponsor you the process will be the same, shorter, and with an labor certification and I-140 rather than I-130. Alternatively you could marry some other US Citizen. Just keep receipts that your first marriage was legit while it lasted. I will point out that parent's naturalization after an F-2B I-130 has already been filed and the beneficiary remains unmarried is not a detriment. Section 6 of CSPA (INA 204(k)) lets the beneficiary opt out at any point of the upgrade from F2B to F1. So in this case it's their choice whether they want to be treated as an F1 or F2B.

Unless your relative is a man under the age of 26 and US gets into a major war requiring a draft sometime soon I wouldn't worry about it. This will literally never come up. In the exceptionally unlikely scenario that it does, if he wants to claim conscientious objector status then really nobody will dig up his N-400 to say "In 2022 you checked yes for #48 on your N-400", where even if that were to happen the correct answer would be "Yeah, I developed a much more pacifist view since then due to [whatever, religion, all the gun violence, etc, etc], put me into army corps of engineers or some other noncombat role".