How to send .apk file over mobile Gmail? Since .apk is a regular executable file, I was more than sure that I will be able to trick mobile Gmail in the same way as I was able to trick PC version of Gmail years ago to force it to send a PC executable (.exe) which it prevented as well. Turned out, I was wrong.
Usually changing file extension to .dat or some other or compressing it with password (encrypting  file) was enough for PC version of Gmail.
However, for mobile version, everything that I have ready at a hand and tried failed as well:

sending as plain file (obviously),

changing .apk extension to .dat or some other,

compressing with ZIP with no password,

compressing with ZIP (ultra compression) and encrypting archive with a password,

compressing with 7ZIP (ultra compression) and encrypting archive with a password,

using an 7 years old idea of double compression:

compress .apk file into .zip file without password,
compress resulting .zip file again into another .zip file with password / encryption.



If mobile Gmail is able to detect that I am sending .apk executable file even in 7zip compressed file with password (or it can prevent me from sending such file for any other reasons) do I have any option left? Is there any way to send .apk file over mobile Gmail (attach them to message composed in mobile Gmail)?
Blocking .apk files and encrypted archives as email attachments is clearly mentioned in GMail policy:

To protect you against potential viruses and harmful software, Gmail doesn't allow you to attach certain types of files, including:
...

Password protected archives whose content is an archive



To protect your account, Gmail doesn't allow you to attach certain types of files...:
.ade, .adp, .apk, ...

So no one can help with that except Google. You can go with file sharing as suggested by others here, and Google as well:

If you're sure the file is safe, you can ask the sender to upload the file to Google Drive. Then send it as a Drive attachment.

Source: https://support.google.com/mail/answer/6590
But if email attachment is the only option you want to go with, use GPG/PGP encryption which is very commonly used in emails, even to encrypt whole emails including subject and body. Many e-mail clients provide OpenPGP-compliant email security. On Android you can use Termux or OpenKeychain for GPG file encryption. Both are open-source and free (I've no affiliation with either).