Not obvious to me why that is happening:
ayoub@vboxpwfl:~/testdir$ ls
textfile
ayoub@vboxpwfl:~/testdir$ gpg -r sentry -e textfile
gpg: sentry: skipped: Unusable public key
gpg: textfile: encryption failed: Unusable public key
ayoub@vboxpwfl:~/testdir$ gpg --list-keys
/home/ayoub/.gnupg/pubring.kbx
------------------------------
pub ed25519 2020-07-09 [SC] [expires: 2020-09-25]
3C5B212A55B966881E2D2718A45398B520BEE91E
uid [ultimate] sentry
pub ed25519 2020-07-09 [SC] [expires: 2021-07-09]
7A675D7F52BC905C22F8249091556BC29D4C595E
uid [ultimate] develop1
sub cv25519 2020-07-09 [E] [expires: 2021-07-09]
ayoub@vboxpwfl:~/testdir$ gpg --list-secret-keys
/home/ayoub/.gnupg/pubring.kbx
------------------------------
sec ed25519 2020-07-09 [SC] [expires: 2020-09-25]
3C5B212A55B966881E2D2718A45398B520BEE91E
uid [ultimate] sentry
sec ed25519 2020-07-09 [SC] [expires: 2021-07-09]
7A675D7F52BC905C22F8249091556BC29D4C595E
uid [ultimate] develop1
ssb cv25519 2020-07-09 [E] [expires: 2021-07-09]
ayoub@vboxpwfl:~/testdir$
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ayoub@vboxpwfl:~/testdir$ ls
textfile
ayoub@vboxpwfl:~/testdir$ gpg -r sentry -e textfile
gpg: sentry: skipped: Unusable public key
gpg: textfile: encryption failed: Unusable public key
ayoub@vboxpwfl:~/testdir$ gpg --list-keys
/home/ayoub/.gnupg/pubring.kbx
------------------------------
pub ed25519 2020-07-09 [SC] [expires: 2020-09-25]
3C5B212A55B966881E2D2718A45398B520BEE91E
uid [ultimate] sentry
pub ed25519 2020-07-09 [SC] [expires: 2021-07-09]
7A675D7F52BC905C22F8249091556BC29D4C595E
uid [ultimate] develop1
sub cv25519 2020-07-09 [E] [expires: 2021-07-09]
ayoub@vboxpwfl:~/testdir$ gpg --list-secret-keys
/home/ayoub/.gnupg/pubring.kbx
------------------------------
sec ed25519 2020-07-09 [SC] [expires: 2020-09-25]
3C5B212A55B966881E2D2718A45398B520BEE91E
uid [ultimate] sentry
sec ed25519 2020-07-09 [SC] [expires: 2021-07-09]
7A675D7F52BC905C22F8249091556BC29D4C595E
uid [ultimate] develop1
ssb cv25519 2020-07-09 [E] [expires: 2021-07-09]
ayoub@vboxpwfl:~/testdir$
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