Rather than quit or retire, I lingered in hopes of being laid off (letting my high pay level, ageism and existing "we don't need Senior Engineers; we have really smart management to do the thinking ahead etc. for the junior engineers" attitudes run their natural course). I "achieved" being laid off 4 months ago at age 58 and collected a nice (9 months' pay) severance package as a precursor to (this month) finally deciding to retire.
I still loved (and was/am capable of) doing the work, but having gone another few rounds of "Leetcode interview process" in the past few months, and having realized that I've reached the end of my willingness to tolerate what seems to be near-pervasive "Agile cargo-cult ceremony" (and everywhere, "Agile is whatever we decide it is") and (less pervasive but still frequently encountered) technically clueless headline-chasing (micro-)management in the presence of increasing active monitoring/collection of (remote) employee activity metrics and pervasive exhortations (mapped to KPIs) to "deliver innovation!" and "do it together!". Why run the Leetcode gauntlet (which seems to closely resemble Final Exams Week from my Uni days, with the same intense cramming prerequisite) only to land in a team/management circumstance of uncertain quality (bail out and do it again?)?
Likewise I've realized that maintaining my W2 income via FTE at my age and position would mostly serve to raise my tax bracket and preclude me from taking minimally taxed withdrawals from my IRA starting in a few months (these have to be taken sometime, and the less taxation, the better).
The process of "letting go" of my working career and adopting a true retirement mindset has taken me at least the past 4 months (I might not be done with it yet), because I do really love and have excelled at the hands-on work (and being self-taught and very motivated to stay abreast of much of what is changing for the better in SW Dev, I've been operating in long-term independent self-study mode for my entire career, turning this background process off is proving challenging).