Add comment about reCAPTCHA v3

Author: vbaranov

setup/env-variables/backend-env-variables.md

@@ -435,15 +435,15 @@ See the [Time format](backend-env-variables.md#time-format) section for more inf
 ## <mark style="background-color:orange;">CSV Export</mark>
 
 {% hint style="info" %}
-reCAPTCHA v2 and v3 keys for CSV export page. Do not use both v2/v3 keys. Only one version of reCAPTCHA should be used.
+reCAPTCHA v2 and v3 keys for CSV export page. Do not use both v2/v3 keys. Only one version of reCAPTCHA should be used. Use Invisible reCAPTCHA v2 for the latest versions. reCAPTCHA v3 support may be discontinued in future updates.
 {% endhint %}
 
 | Variable                     | Description                                                                                                                                                                                                      | Parameters                                                                  |
 | ---------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------- |
 | `RE_CAPTCHA_SECRET_KEY`      | Google reCAPTCHA v2 secret key. Used by advanced CSV export. Implemented in [#4747](https://github.com/blockscout/blockscout/pull/4747)                                                                          | <p>Version: v4.0.0+<br>Default: (empty)<br>Applications: API</p>            |
 | `RE_CAPTCHA_CLIENT_KEY`      | Google reCAPTCHA v2 client key. Used by advanced CSV export. Implemented in [#4747](https://github.com/blockscout/blockscout/pull/4747)                                                                          | <p>Version: v4.0.0+<br>Default: (empty)<br>Applications: API</p>            |
-| `RE_CAPTCHA_V3_SECRET_KEY`   | Google reCAPTCHA v3 secret key. Used by advanced CSV export. Implemented in [#7273](https://github.com/blockscout/blockscout/pull/7273)                                                                          | <p>Version: v5.1.4+<br>Default: (empty)<br>Applications: API</p>            |
-| `RE_CAPTCHA_V3_CLIENT_KEY`   | Google reCAPTCHA v3 client key. Used by advanced CSV export. Implemented in [#7273](https://github.com/blockscout/blockscout/pull/7273)                                                                          | <p>Version: v5.1.4+<br>Default: (empty)<br>Applications: API</p>            |
+| `RE_CAPTCHA_V3_SECRET_KEY`   | **Only compatible with frontend version v1.36.x. For later versions, use Invisible reCAPTCHA v2.** Google reCAPTCHA v3 secret key. Used by advanced CSV export. Implemented in [#7273](https://github.com/blockscout/blockscout/pull/7273)                                                                          | <p>Version: v5.1.4+<br>Default: (empty)<br>Applications: API</p>            |
+| `RE_CAPTCHA_V3_CLIENT_KEY`   | **Only compatible with frontend version v1.36.x. For later versions, use Invisible reCAPTCHA v2.** Google reCAPTCHA v3 client key. Used by advanced CSV export. Implemented in [#7273](https://github.com/blockscout/blockscout/pull/7273)                                                                          | <p>Version: v5.1.4+<br>Default: (empty)<br>Applications: API</p>            |
 | `RE_CAPTCHA_DISABLED`        | Disable reCAPTCHA. Implemented in [#7416](https://github.com/blockscout/blockscout/pull/7416)                                                                                                                    | <p>Version: v5.1.5+<br>Default: <code>false</code><br>Applications: API</p> |
 | `RE_CAPTCHA_CHECK_HOSTNAME`  | Disable reCAPTCHA hostname check. More details on [reCaptcha docs](https://developers.google.com/recaptcha/docs/domain_validation). Implemented in [#10706](https://github.com/blockscout/blockscout/pull/10706) | <p>Version: v6.9.0+<br>Default: <code>false</code><br>Applications: API</p> |
 | `CSV_EXPORT_LIMIT`           | Changes max number of rows in CSV export. Implemented in [#10497](https://github.com/blockscout/blockscout/pull/10497)                                                                                           | <p>Version: v6.8.0+<br>Default: <code>10000</code><br>Applications: API</p> |