The Proton Mail app on linux is very, very resource heavy, over the 100%. The fan starts to blow immediately when starting Proton, see the top listing below.

PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND                                                                                                           

20308 eelco 20 0 1393,9g 265164 147488 S 100,3 1,7 5:57.12 Proton Mail Bet

20484 eelco 20 0 1427,7g 895700 115368 S 49,9 5,8 3:05.88 Proton Mail Bet

20359 eelco 20 0 32,4g 82256 65280 S 10,3 0,5 0:35.57 Proton Mail Bet