EXCEL 365 on MacBook Air 2020 (INTEL) is very buggy

When I am using EXCEL 365 on my MacBook Air 2020 (INTEL), I find that there are a lot of bugs. For example:

1. more than 50% of the time, the keyboard shortcuts are not working. Sometimes, when I use Cntr-C to copy a cell, but the CMD-Cntr-V (Paste Special) does not work and I have to use the pull-down menu.
2. about 50% of the time, the Replace function does not replace. Say I wish to replace a comma (,) in a cell with an empty space, I hit the Cntr-H and click Replace/Replace ALL, nothing happens. I have to repeat the above one more time to make it work.
3. FILL DOWN. about 50% of the time, when I use FILL DOWN, the cells are not changing.

Just want to know if you guys have similar problems and appreciate it very much if you could point me to possible solutions.