Excel 365 is UNUSABLE for professional work — performance has catastrophically degraded

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Thank you, m_tarler​ and Detlef_Lewin​ , for the inputs. I'm very aware that this site is not an official Microsoft feedback site (I already posted the same complaint there - but I'm not expecting any response from them).

One overall point: I have been working with the same template for, literally, 20 years, between 8 and 12 hours a day. I'm not "new to Excel". Nor is this a problem with "one spreadsheet" - I'm having the same issue on all my spreadsheets on two machines. Excel was always a mediocre tool, but now it is unbearable to work with. My productivity is at 20% of its usual level.

So the questions/suggestions with my answers:

- What is the number of objects (shapes, charts, pictures, icons, etc.) in your sheet?

Not many - see the picture below. Pressing ALT+F10 (for those that might try the same) gave me the number of objects (on the right). If I try to drag Oval 39 with Line 36 (two very simple objects), Excel will blink, display a message that it is not responding, and, after some struggle, move the object.

- Have you tried to run the Check Performance function (under the 'Review' tab)?

My workbooks don't have incorrect calculations or corruption, as it is impossible for me to mess up with 70+ similar models. If I run Check Performance, it mostly complains about cell formatting (note on the picture below that my models have a dark background - it is impossible to work the hours I do with a bright-white screen)

- Have you tried changing from Automatic to Manual Calculations (under Calculations on the Formulas tab)?

All my models have manual calculations by default. Most valuation models (if you are trying to properly determine an adequate debt level) are circular, so I set them to manual mode to avoid wasting time on constant calculations.

- Do you notice this issue with other workbooks?

Yes - every single workbook has the same issue. Excel is slow with all of them, even relatively simple ones. And it is NOT my machine: I tested in two of them, turning-off add-ins (I use FactSet, for instance), running Excel in Safe Mode, moving back to other releases (but maybe I will go back a few months, to see what happens). Nothing worked.

- Have you tried copying the key formulas and pasting them into a new 'clean' workbook?

See how many tabs I have in each model (in the picture below). It is basically impossible to copy and paste these models into other models. It would take me months to do so. And it would defeat the purpose of using Excel.

- Some other considerations that should be investigated include making sure there are no circular references, bad external references/link/data, minimize the use of conditional formatting, minimize the use of volatile functions

Circular references (as I discussed above) are inevitable. But again, I have been working with them for more than 20 years. I do use OFFSET, INDEX/MATCH, among others. But saying "don't use anything complex" defeats the purpose - in 2025 - of having powerful computers. I can't use Excel as a simple spreadsheet that performs addition, subtraction, multiplication, or division. If that is the case, I'd better investigate using Lotus 1-2-3! :) I will investigate the use of LAMBDA - it could make a few calculations more elegant.

I suspect that Microsoft is messing up with chart rendering. I say that because worksheets with charts scroll down very, very slowly. Maybe charts are being rendered constantly even when they are not shown. It could also explain the delay when I press ALT (not that the menus are hidden in the picture below - I don't use menus nor toolbars, as I memorized all the keyboard shortcuts I need).

Last, thank you very much for taking the time to help me. Hopefully, I will find a solution. And maybe someone from Microsoft will see this thread and reach out.