I did a bit more sleuthing, and can add on the following.
According to: https://github.com/MiSTer-devel/Downloader_MiSTer
I should d/l into my /Scripts folder "downloader.sh". Interestingly, I have never had this script. Rather, my Update_all.sh appears to be identical to downloader.sh (maybe a name-change occurred at some point)?
Further, the above site shows the default params for /media/fat/downloader.ini, which are very different than the params I have had in there since day 1. Again, this setup worked just fine for 2+ years, up until updating today. In case it is useful, here are the contents of my "downloader.ini":
[mister]
filter = !cheats !computer-cores x68000 !alternatives !hbmame !handheld2p !extra-utilities !arcade-astrocade !acornatom !acornelectron !adam !apogee !atari800 !adventurevision !arcadia !astrocade !ay-3-8500 !channelf !odyssey2 !vc4000 !vectrex !altair8800 !amstrad !amstrad-pcw !alicemc10 !aquarius !archie !avision !bbcmicro !bk0011m !coco2 !coco3 !edsac !epochgalaxyii !galaksija !interact !jupiter !lynx48 !laser !c16 !c64 !ondra_spo186 !orao !oric !pdp1 !pet2001 !pmd85 !ql !rx78 !samcoupe !sharpmz !sordm5 !spectrum !spmx !svi328 !tatungeinstein !ti-99_4a !trs-80 !tsconf !uk101 !vector06 !vic20 !zx81 !zxnext !atari5200 !atarilynx !atarist !coleco !colecoadam !colecovision !gamate !gameoflife !gamenwatch !gnw !intellivision !s32x !supervision !casio_pv-1000 !casio_pv-2000 !creativision !mgl !gameboycolor !atari2600 !wonderswancolor !gamegear !pokemonmini
[distribution_mister]
db_url = https://raw.githubusercontent.com/MiSTe ... b.json.zip
[jtcores]
db_url = https://raw.githubusercontent.com/joteg ... b.json.zip
[theypsilon_unofficial_distribution]
db_url = https://raw.githubusercontent.com/theyp ... b.json.zip
[names_txt]
db_url = https://raw.githubusercontent.com/Three ... on_US.json
[bios_db]
db_url = https://raw.githubusercontent.com/BigDe ... b.json.zip
[Coin-OpCollection/Distribution-MiSTerFPGA]
db_url = https://raw.githubusercontent.com/Coin- ... b.json.zip
[arcade_names_txt]
db_url = https://raw.githubusercontent.com/PigSa ... es_US.json
Please also find my "downloader.log" file attached. Potentially of note, I see that "UPDATE_LINUX = false" which isn't the recommended setting. I have no idea how to change this to "true"...
thanks again