Is it impossible to access old Google accounts even with access to all credentials (no 2FA set up)?

I have two old Google/Gmail accounts which I haven’t used in a long time. I’ve been trying to log into them again on several occasions over the past few months (even using different browsers), without success. These accounts were created before two-factor authentication (2FA) really existed for Google accounts, so they have neither a 2FA app/token nor even a phone number associated with them.

Since I’m no longer signed into these accounts anywhere (and haven’t been for years), and there’s no 2FA, Google apparently finds my completely valid login attempts suspicious and doesn’t let me access my own accounts! What happens is as follows:

1. I go to accounts.google.com and enter my Gmail address.
2. I enter the (correct!) password.
3. Google says “Verify it’s you. This device isn’t recognized. For your security, Google wants to make sure it’s really you.”…
4. …and asks for the recovery email address associated with the account.
5. I enter the (correct!) recovery email address (which I still have access to as well).
6. Google asks for “a phone number to get a text message with a verification code.” (Not sure what the point of this is, since I can literally supply any phone number here.)
7. I enter my phone number.
8. Google says “A text message with a 6-digit verification code was just sent to [my phone number].” and asks for the code.
9. I enter the 6-digit code which I received from Google via SMS.
10. I get the following page:

I’ve tried Google Account Recovery as well, with the same result.

To summarize:

• I know the correct password to my account.
• I know the correct recovery email address for my account and still have access to that address.
• There is no phone number associated with the account.
• 2FA is not enabled for the account.

This all seems very Kafkaesque! Why can’t I sign in? Is there a way to solve this?