Start with the right checks.
A short period of activity after signing in can differ from a Mac that stays unusable. Note the timing, applications and whether the issue settles without repeated restarts.
What to do next.
Record how long the slowdown lasts and whether it happens at every sign in.
Check available storage and whether an application is restoring many windows or a large working session.
Use Activity Monitor as an observation tool if you are comfortable with it. Do not stop an unfamiliar process just because its usage is high.
Check whether the applications you need meet the Mac’s hardware and macOS requirements, using their official documentation.
Check the result.
Try the same everyday task after startup activity settles. Keep observations from a normal session and a slow one for comparison.
Stop and get help if…
The Mac crashes, reports storage errors or remains slow throughout the day. A recurring problem needs investigation before replacing equipment or purchasing a cleanup tool.