gpg 1.4.23 works: "gpg -d test.txt.gpg"
gpg 2.2.20 doesn't work: "gpg2 -d test.txt.gpg"
"gpg -vv --debug-level 8 -d test.txt.gpg" gives, in addition to what the gpg command outputs:
gpg: decryption failed: No secret key
gpg: keydb: handles=2 locks=0 parse=0 get=2
gpg: build=0 update=0 insert=0 delete=0
gpg: reset=0 found=2 not=1 cache=0 not=0
gpg: kid_not_found_cache: count=0 peak=0 flushes=0
gpg: sig_cache: total=42 cached=42 good=42 bad=0
gpg: random usage: poolsize=600 mixed=0 polls=0/0 added=0/0
outmix=0 getlvl1=0/0 getlvl2=0/0
gpg: rndjent stat: collector=0x0000000000000000 calls=0 bytes=0
gpg: secmem usage: 0/32768 bytes in 0 blocks
There are also a few hundred DBG lines regarding search.keyring.c.1109 and parse.keyring.c.415
gpg (GnuPG) 2.2.20
libgcrypt 1.8.5
Slackware-current, kernel 5.4.30