I've just done probate and IHT for both my parents, and as long as you keep track of everything it really wasn't hard.
Dad died first (March) and all the IHT and probate was online, so once I had all the figures on their savings accounts etc I got the IHT and probate done in one evening - everything was left to mum, so none of his IHT allowance was used at all (£375k personal allowance plus £175k property)
Mum died 32 days after him, leaving everything to her children. This time I had to do the IHT on actual forms as I was using the allowance transfer, but the checklist on the main form is great, and it was all very clear if you worked through systematically.
Dads probate came back in 30 days, mums in 14 (I had advised them that she had died when I put dads in, so some checks may have been done at the same time)
My top tips
As soon as someone dies and you'll be doing the arrangements, get a notebook or make an Excel doc with all the information you might possibly need - I didn't expect to need to know where my parents got married, and I had to give their dates of birth, NI numbers, my NI number etc etc so many times and having one place where I had everything together was great
Make a tracking sheet so you have a list of all the people you have talked to, which documents are with who, and next steps.
Google bereavement services for each company/bank you need to deal with - they've all been super helpful and made it easy to understand what is needed.
Get multiple copies (5) of the death certificate as some places are really, really slow at sending things back at the moment.
When applying for probate, additional copies are only £1.50 each, so again, get extras
Make a tracking list of all the possible sources of income, and possible estate debts, then note when you are given a figure, when you apply for things to be paid, and then when received
If there are other beneficiaries, everyone wants their money etc, but as executor your duty is to the estate, and remember that you need to be ready in case a debt pops up, so don't be rushed.
You can't seem to get executor accounts now, so I opened an online account to get everything paid into so at least it was separate. Cheques have been an issue in these times, so I had to pay into my current account using the app and then transfer to the estate account
The IHT forms can be filled in online, but not saved. If you have a PDF printer on your PC, then you can save your completed form, and this generally makes things easier as solicitors etc for the house sale also did this
I should be totally done with the estate, including selling the house (touch wood) in a months time, and there is no way I could have justified paying what a solicitors would have charged for the amount of work