Windows 10 Pro 32 bit (all updates), Thunderbird portable 102.1.2 (updated and also new clean install.).
I created a new Gmail-account (pop3) whose messages are saved in the global inbox; this setting is saved. I check the mails manually.
Now I want this account to be included when manually fetching messages, and checked the corresponding box in the server settings/advanced of the account:
Tools / Account Settings / ACCOUNT NAME / Server Settings / Advanced / "Include this server when getting new mail".
If I then close the advanced account settings and then open it again, the checkmark is no longer checked, which means the setting cannot be saved. Manually retrieving messages works.
I got the bug with version 102.1.2 portable. Now I've tried installing the regular (non-portable) 32-bit version 102.1.2 on my test computer, and it works!
So this bug only seems to be with the portable version.
I found the bug in the updated German and also the clean installed English version of Thunderbird portable 102.1.2.