Access log:
localhost - - [04/Jan/2023:11:05:10 +0100] "POST / HTTP/1.1" 200 349 Create-Printer-Subscriptions successful-ok
localhost - - [04/Jan/2023:11:05:10 +0100] "POST / HTTP/1.1" 200 176 Create-Printer-Subscriptions successful-ok
localhost - - [04/Jan/2023:12:42:38 +0100] "POST / HTTP/1.1" 401 123 Cancel-Subscription successful-ok
localhost - root [04/Jan/2023:12:42:38 +0100] "POST / HTTP/1.1" 200 123 Cancel-Subscription successful-ok
localhost - - [04/Jan/2023:12:42:38 +0100] "POST / HTTP/1.1" 200 152 Cancel-Subscription successful-ok
localhost - - [04/Jan/2023:16:38:46 +0100] "POST / HTTP/1.1" 200 349 Create-Printer-Subscriptions successful-ok
localhost - - [04/Jan/2023:16:38:46 +0100] "POST / HTTP/1.1" 200 176 Create-Printer-Subscriptions successful-ok
localhost - - [04/Jan/2023:16:38:56 +0100] "POST / HTTP/1.1" 200 173 Create-Printer-Subscriptions successful-ok
localhost - - [04/Jan/2023:18:18:07 +0100] "POST /printers/MFCJ6530DW HTTP/1.1" 200 553443 Print-Job successful-ok
localhost - - [04/Jan/2023:18:18:08 +0100] "POST / HTTP/1.1" 200 371 Create-Printer-Subscriptions successful-ok
localhost - - [04/Jan/2023:18:20:31 +0100] "POST / HTTP/1.1" 200 282 Create-Printer-Subscriptions successful-ok
localhost - - [04/Jan/2023:18:20:41 +0100] "POST /admin/ HTTP/1.1" 401 165 CUPS-Set-Default successful-ok
localhost - cups-pk-helper [04/Jan/2023:18:20:41 +0100] "POST /admin/ HTTP/1.1" 200 165 CUPS-Set-Default successful-ok
localhost - - [04/Jan/2023:18:20:41 +0100] "GET /admin/conf/lpoptions HTTP/1.1" 401 0 - -
localhost - mypc [04/Jan/2023:18:20:41 +0100] "GET /admin/conf/lpoptions HTTP/1.1" 200 0 - -
localhost - mypc [04/Jan/2023:18:20:41 +0100] "GET /admin/conf/lpoptions HTTP/1.1" 200 4618 - -
localhost - - [04/Jan/2023:18:20:43 +0100] "POST / HTTP/1.1" 200 161 Cancel-Subscription successful-ok
localhost - cups-pk-helper [04/Jan/2023:18:20:48 +0100] "POST /jobs/ HTTP/1.1" 200 149 Cancel-Job successful-ok
localhost - - [04/Jan/2023:18:21:14 +0100] "POST /printers/MFCJ6530DW HTTP/1.1" 200 18067 Print-Job successful-ok
BrotherMFC-J6530DW printer set as default but nothing changed.
Now I do the other test.
The cupsd.conf file contains 4 times the configuration you indicated to me but they are all correctly set to default.