I made a release apk using buildozer android release command. Then I sign and zipalign my apk using following commands.
genarate keystore file [before] - keytool -genkey -v -keystore myapp.keystore -alias myalias -keyalg RSA -keysize 2048 -validity 10000
generate keystore file [after] -  keytool -importkeystore -srckeystore myapp.keystore -destkeystore myapp.keystore -deststoretype pkcs12
sign apk - jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore myapp.keystore myapp-0.1-arm64-v8a-release-unsigned.apk myalias
zipalign apk -  zipalign -v 4 myapp-0.1-arm64-v8a-release-unsigned.apk playstore-release.apk
After everything done play store gives this error - You uploaded an APK with an invalid signature (learn more about signing). Error from apksigner: ERROR: MIN_SIG_SCHEME_FOR_TARGET_SDK_NOT_MET: Target SDK version 30 requires a minimum of signature scheme v2; the APK is not signed with this or a later signature scheme
target max api 30 and min api 21, sdk 30 used
How i upload my apk to playstore in 2021
First, your project must be able to run on an android with .apk on debug and unsigned mode.
If it's the case you can read theses 2 steps.
First you must signed your application to be sure that you are the only one that can update it (prevent from malicious algo insertion).
Change this in your buildozer.spec file:
#App store ask us to have this architecture and the latest api available (actually 29)
android.arch = arm64-v8a
android.api = 29
#Each time you update your apk on the app store, you have to incremente this variable by 1. It's 8211 by default BUT BE AWARE, you have to change it from the start (I begin with 1):
android.numeric_version = 1

Now that your key is signed, go on the terminal and:
---- FULFILL FOLLOWING VARIABLES ----
project_path=~/MY/PATH
key_filename=mykeyfilename
key_alias=mykeyaliasname
password="turlututu"
---- TO DO ONLY ONE TIME ----
mkdir -p ~/keystores/
keytool -genkey -v -keystore ~/keystores/$key_filename.keystore -alias $key_alias -keyalg RSA -keysize 2048 -validity 10000
---- a warning is printed and advice us to migrate to PKCS12 so we do it ----
keytool -importkeystore -srckeystore ~/keystores/$key_filename.keystore -destkeystore ~/keystores/$key_filename.keystore -deststoretype pkcs12
---- ENDING OF THE PART TO DO ONLY ONE TIME ----
export P4A_RELEASE_KEYSTORE=~/keystores/$key_filename.keystore
export P4A_RELEASE_KEYSTORE_PASSWD=$password
export P4A_RELEASE_KEYALIAS_PASSWD=$password
export P4A_RELEASE_KEYALIAS=$key_alias
cd $project_path
buildozer -v android release
Error while signing an kivy app for the play store