I can confirm the following based on my own recent experiences.

1. REPSOL - I don't use the Repsol App. I ask the cashier to scan my IB Plus card from the IB App. It has become so efficient now that my last 3
fuel ups have been credited to my IB Avios within a few hours. I also always pay using my Amex card for a "double hit".

2. ENDESA - My electricity contract is indeed with Endesa. Their website isn't the greatest thing in the world, but if you are patient enough to finally
see the Iberia Plus page and put your details in then it definitely works. EVERY month I receive 50 Avios regular as clockwork.

3. HOTEL bookings via Booking.com - In August I completed a hotel stay in Madrid and another one in Geneva. Both these stays finally got credited today. (ie. 2 months after)
Watch out! The Credit date is the Check-Out date of the hotel stay. Booking.com handles it hotel accounts always "after" the hotel stay so making a duff booking
in my opinion won't get you any Avios.

4. AMEX - Anytime I transfer Amex MR points into IB Plus Avios the transfer is always completed with a day.